Maize variety inbred PH18K6

ABSTRACT

A novel maize variety designated PH18K6 and seed, plants and plant parts thereof. Methods for producing a maize plant that comprise crossing maize variety PH18K6 with another maize plant. Methods for producing a maize plant containing in its genetic material one or more traits introgressed into PH18K6 through backcross conversion and/or transformation, and to the maize seed, plant and plant part produced thereby. Hybrid maize seed, plant or plant part produced by crossing the variety PH18K6 or a locus conversion of PH18K6 with another maize variety.

FIELD OF THE INVENTION

This invention relates generally to the field of maize breeding,specifically relating to an inbred maize variety designated PH18K6.

BACKGROUND OF THE INVENTION

The goal of plant breeding is to combine, in a single variety or hybrid,various desirable traits. For field crops, these traits may includeresistance to diseases and insects, resistance to heat and drought,reducing the time to crop maturity, greater yield, and better agronomicquality. With mechanical harvesting of many crops, uniformity of plantcharacteristics such as germination, stand establishment, growth rate,maturity, plant height and ear height, is important. Traditional plantbreeding is an important tool in developing new and improved commercialcrops.

SUMMARY OF THE INVENTION

According to the invention, there is provided a novel maize variety,designated PH18K6 and processes for making PH18K6. This inventionrelates to seed of maize variety PH18K6, to the plants of maize varietyPH18K6, to plant parts of maize variety PH18K6, and to processes formaking a maize plant that comprise crossing maize variety PH18K6 withanother maize plant. This invention also relates to processes for makinga maize plant containing in its genetic material one or more traitsintrogressed into PH18K6 through backcross conversion and/ortransformation, and to the maize seed, plant and plant parts producedthereby. This invention further relates to a hybrid maize seed, plant orplant part produced by crossing the variety PH18K6 or a locus conversionof PH18K6 with another maize variety.

DEFINITIONS

Certain definitions used in the specification are provided below. Alsoin the examples that follow, a number of terms are used herein. In orderto provide a clear and consistent understanding of the specification andclaims, including the scope to be given such terms, the followingdefinitions are provided. NOTE: ABS is in absolute terms and % MN ispercent of the mean for the experiments in which the inbred or hybridwas grown. PCT designates that the trait is calculated as a percentage.% NOT designates the percentage of plants that did not exhibit a trait.For example, STKLDG % NOT is the percentage of plants in a plot thatwere not stalk lodged. These designators will follow the descriptors todenote how the values are to be interpreted. Below are the descriptorsused in the data tables included herein.

ABIOTIC STRESS TOLERANCE: resistance to non-biological sources of stressconferred by traits such as nitrogen utilization efficiency, alterednitrogen responsiveness, drought resistance, cold, and salt resistance

ABTSTK=ARTIFICIAL BRITTLE STALK: A count of the number of “snapped”plants per plot following machine snapping. A snapped plant has itsstalk completely snapped at a node between the base of the plant and thenode above the ear. Expressed as percent of plants that did not snap.

ALLELE: Any of one or more alternative forms of a genetic sequence. In adiploid cell or organism, the two alleles of a given sequence typicallyoccupy corresponding loci on a pair of homologous chromosomes.

ALTER: The utilization of up-regulation, down-regulation, or genesilencing.

ANTHESIS: The time of a flower's opening.

ANTIOXIDANT: A chemical compound or substance that inhibits oxidation,including but not limited to tocopherol or tocotrienols.

ANT ROT=ANTHRACNOSE STALK ROT (Colletotrichum graminicola): A 1 to 9visual rating indicating the resistance to Anthracnose Stalk Rot. Ahigher score indicates a higher resistance. Data are collected only whensufficient selection pressure exists in the experiment measured.

BACKCROSSING: Process in which a breeder crosses a hybrid progenyvariety back to one of the parental genotypes one or more times.

BACKCROSS PROGENY: Progeny plants produced by crossing PH18K6 withplants of another maize line that comprise a desired trait or locus,selecting F1 progeny plants that comprise the desired trait or locus,and crossing the selected F1 progeny plants with the PH18K6 plants 1 ormore times to produce backcross progeny plants that comprise said traitor locus.

BARPLT=BARREN PLANTS: The percent of plants per plot that were notbarren (lack ears).

BLUP=BEST LINEAR UNBIASED PREDICTION. The BLUP values are determinedfrom a mixed model analysis of hybrid performance observations atvarious locations and replications. BLUP values for inbred maize plants,breeding values, are estimated from the same analysis using pedigreeinformation.

BORBMN=ARTIFICIAL BRITTLE STALK MEAN: The mean percent of plants not“snapped” in a plot following artificial selection pressure. A snappedplant has its stalk completely snapped at a node between the base of theplant and the node above the ear. Expressed as percent of plants thatdid not snap. A high number is good and indicates tolerance to brittlesnapping.

BRENGMN=BRITTLE STALK ENERGY MEAN: The mean amount of energy per unitarea needed to artificially brittle snap a corn stalk. A high number isgood and indicates tolerance to brittle snapping.

BREEDING: The genetic manipulation of living organisms.

BREEDING CROSS: A cross to introduce new genetic material into a plantfor the development of a new variety. For example, one could cross plantA with plant B, wherein plant B would be genetically different fromplant A. After the breeding cross, the resulting F1 plants could then beselfed or sibbed for one, two, three or more times (F1, F2, F3, etc.)until a new inbred variety is developed.

BREEDING VALUE: A relative value determined by evaluating the progeny ofthe parent. For corn the progeny is often the F1 generation and theparent is often an inbred variety.

BRLPNE=ARTIFICIAL ROOT LODGING EARLY SEASON: The percent of plants notroot lodged in a plot following artificial selection pressure appliedprior to flowering. A plant is considered root lodged if it leans fromthe vertical axis at an approximately 30 degree angle or greater.Expressed as percent of plants that did not root lodge. A high number isgood and indicates tolerance to root lodging.

BRLPNL=ARTIFICIAL ROOT LODGING LATE SEASON: The percent of plants notroot lodged in a plot following artificial selection pressure duringgrain fill. A plant is considered root lodged if it leans from thevertical axis at an approximately 30 degree angle or greater. Expressedas percent of plants that did not root lodge. A high number is good andindicates tolerance to root lodging.

BRTSTK=BRITTLE STALKS: This is a measure of the stalk breakage near thetime of pollination, and is an indication of whether a hybrid or inbredwould snap or break near the time of flowering under severe winds. Dataare presented as percentage of plants that did not snap. Data arecollected only when sufficient selection pressure exists in theexperiment measured.

BRTPCN=BRITTLE STALKS: This is an estimate of the stalk breakage nearthe time of pollination, and is an indication of whether a hybrid orinbred would snap or break near the time of flowering under severewinds. Data are presented as percentage of plants that did not snap.Data are collected only when sufficient selection pressure exists in theexperiment measured.

CARBOHYDRATE: Organic compounds comprising carbon, oxygen and hydrogen,including sugars, starches and cellulose.

CELL: Cell as used herein includes a plant cell, whether isolated, intissue culture or incorporated in a plant or plant part.

CLDTST=COLD TEST: The percent of plants that germinate under cold testconditions.

CLN═CORN LETHAL NECROSIS: Synergistic interaction of maize chloroticmottle virus (MCMV) in combination with either maize dwarf mosaic virus(MDMV-A or MDMV-B) or wheat streak mosaic virus (WSMV). A 1 to 9 visualrating indicating the resistance to Corn Lethal Necrosis. A higher scoreindicates a higher resistance. Data are collected only when sufficientselection pressure exists in the experiment measured.

CMSMT=COMMON SMUT: This is the percentage of plants not infected withCommon Smut. Data are collected only when sufficient selection pressureexists in the experiment measured.

COMRST=COMMON RUST (Puccinia sorghi): A 1 to 9 visual rating indicatingthe resistance to Common Rust. A higher score indicates a higherresistance. Data are collected only when sufficient selection pressureexists in the experiment measured.

CROSS POLLINATION: Fertilization by the union of two gametes fromdifferent plants.

CROSSING: The combination of genetic material by traditional methodssuch as a breeding cross or backcross, but also including protoplastfusion and other molecular biology methods of combining genetic materialfrom two sources.

D and D1-Dn: represents the generation of doubled haploid.

D/D=DRYDOWN: This represents the relative rate at which a hybrid willreach acceptable harvest moisture compared to other hybrids on a 1 to 9rating scale. A high score indicates a hybrid that dries relatively fastwhile a low score indicates a hybrid that dries slowly.

DIGENG=DIGESTIBLE ENERGY: Near-infrared transmission spectroscopy, NIT,prediction of digestible energy.

DIPERS=DIPLODIA EAR MOLD SCORES (Diplodia maydis and Diplodiamacrospora): A 1 to 9 visual rating indicating the resistance toDiplodia Ear Mold. A higher score indicates a higher resistance. Dataare collected only when sufficient selection pressure exists in theexperiment measured.

DIPLOID PLANT PART: Refers to a plant part or cell that has the samediploid genotype as PH18K6.

DIPROT=DIPLODIA STALK ROT SCORE: Score of stalk rot severity due toDiplodia (Diplodia maydis). Expressed as a 1 to 9 score with 9 beinghighly resistant. Data are collected only when sufficient selectionpressure exists in the experiment measured.

DRPEAR=DROPPED EARS: A measure of the number of dropped ears per plotand represents the percentage of plants that did not drop ears prior toharvest. Data are collected only when sufficient selection pressureexists in the experiment measured.

D/T=DROUGHT TOLERANCE: This represents a 1 to 9 rating for droughttolerance, and is based on data obtained under stress conditions. A highscore indicates good drought tolerance and a low score indicates poordrought tolerance. Data are collected only when sufficient selectionpressure exists in the experiment measured.

EARHT=EAR HEIGHT: The ear height is a measure from the ground to thehighest placed developed ear node attachment and is measured in inches.

EARMLD=GENERAL EAR MOLD: Visual rating (1 to 9 score) where a 1 is verysusceptible and a 9 is very resistant. This is based on overall ratingfor ear mold of mature ears without determining the specific moldorganism, and may not be predictive for a specific ear mold. Data arecollected only when sufficient selection pressure exists in theexperiment measured.

EARSZ=EAR SIZE: A 1 to 9 visual rating of ear size. The higher therating the larger the ear size.

EBTSTK=EARLY BRITTLE STALK: A count of the number of “snapped” plantsper plot following severe winds when the corn plant is experiencing veryrapid vegetative growth in the V5-V8 stage. Expressed as percent ofplants that did not snap. Data are collected only when sufficientselection pressure exists in the experiment measured.

ECB1LF=EUROPEAN CORN BORER FIRST GENERATION LEAF FEEDING (Ostrinianubilalis): A 1 to 9 visual rating indicating the resistance topreflowering leaf feeding by first generation European Corn Borer. Ahigher score indicates a higher resistance. Data are collected only whensufficient selection pressure exists in the experiment measured.

ECB21T=EUROPEAN CORN BORER SECOND GENERATION INCHES OF TUNNELING(Ostrinia nubilalis): Average inches of tunneling per plant in thestalk. Data are collected only when sufficient selection pressure existsin the experiment measured.

ECB2SC=EUROPEAN CORN BORER SECOND GENERATION (Ostrinia nubilalis): A 1to 9 visual rating indicating post flowering degree of stalk breakageand other evidence of feeding by second generation European Corn Borer.A higher score indicates a higher resistance. Data are collected onlywhen sufficient selection pressure exists in the experiment measured.

ECBDPE=EUROPEAN CORN BORER DROPPED EARS (Ostrinia nubilalis): Droppedears due to European Corn Borer. Percentage of plants that did not dropears under second generation European Corn Borer infestation. Data arecollected only when sufficient selection pressure exists in theexperiment measured.

ECBLSI=EUROPEAN CORN BORER LATE SEASON INTACT (Ostrinia nubilalis): A 1to 9 visual rating indicating late season intactness of the corn plantgiven damage (stalk breakage above and below the top ear) causedprimarily by 2^(nd) and/or 3^(rd) generation ECB larval feeding beforeharvest. A higher score is good and indicates more intact plants. Dataare collected only when sufficient selection pressure exists in theexperiment measured.

EGRWTH=EARLY GROWTH: This is a measure of the relative height and sizeof a corn seedling at the 2-4 leaf stage of growth. This is a visualrating (1 to 9), with 1 being weak or slow growth, 5 being averagegrowth and 9 being strong growth. Taller plants, wider leaves, moregreen mass and darker color constitute higher score. Data are collectedonly when sufficient selection pressure exists in the experimentmeasured.

ERTLDG=EARLY ROOT LODGING: The percentage of plants that do not rootlodge prior to or around anthesis; plants that lean from the verticalaxis at an approximately 30 degree angle or greater would be counted asroot lodged. Data are collected only when sufficient selection pressureexists in the experiment measured.

ERTLPN=EARLY ROOT LODGING: An estimate of the percentage of plants thatdo not root lodge prior to or around anthesis; plants that lean from thevertical axis at an approximately 30 degree angle or greater would beconsidered as root lodged. Data are collected only when sufficientselection pressure exists in the experiment measured.

ERTLSC=EARLY ROOT LODGING SCORE: Score for severity of plants that leanfrom a vertical axis at an approximate 30 degree angle or greater whichtypically results from strong winds prior to or around floweringrecorded within 2 weeks of a wind event. Expressed as a 1 to 9 scorewith 9 being no lodging. Data are collected only when sufficientselection pressure exists in the experiment measured.

ESSENTIAL AMINO ACIDS: Amino acids that cannot be synthesized de novo byan organism and therefore must be supplied in the diet.

ESTCNT=EARLY STAND COUNT: This is a measure of the stand establishmentin the spring and represents the number of plants that emerge on perplot basis for the inbred or hybrid.

EXPRESSING: Having the genetic potential such that under the rightconditions, the phenotypic trait is present.

EXTSTR=EXTRACTABLE STARCH: Near-infrared transmission spectroscopy, NIT,prediction of extractable starch.

EYESPT=EYE SPOT (Kabatiella zeae or Aureobasidium zeae): A 1 to 9 visualrating indicating the resistance to Eye Spot. A higher score indicates ahigher resistance. Data are collected only when sufficient selectionpressure exists in the experiment measured.

FATTY ACID: A carboxylic acid (or organic acid), often with a longaliphatic tail (long chains), either saturated or unsaturated.

F1 PROGENY: A progeny plant produced by crossing a plant of maizevariety PH18K6 with a plant of another maize line.

FUSERS=FUSARIUM EAR ROT SCORE (Fusarium moniliforme or Fusariumsubglutinans): A 1 to 9 visual rating indicating the resistance toFusarium Ear Rot. A higher score indicates a higher resistance. Data arecollected only when sufficient selection pressure exists in theexperiment measured.

GDU=GROWING DEGREE UNITS: Using the Barger Heat Unit Theory, whichassumes that maize growth occurs in the temperature range 50 degreesF.-86 degrees F. and that temperatures outside this range slow downgrowth; the maximum daily heat unit accumulation is 36 and the minimumdaily heat unit accumulation is 0. The seasonal accumulation of GDU is amajor factor in determining maturity zones.

GDUSHD=GDU TO SHED: The number of growing degree units (GDUs) or heatunits required for an inbred variety or hybrid to have approximately 50percent of the plants shedding pollen and is measured from the time ofplanting. Growing degree units are calculated by the Barger Method,where the heat units for a 24-hour period are:

${G\; D\; U} = {\frac{\left( {{Max}.\mspace{14mu}{temp}.\mspace{11mu}{+ \mspace{11mu}{{Min}.{\mspace{11mu}\;}{temp}.}}} \right)}{2} - 50}$

The units determined by the Barger Method are then divided by 10. Thehighest maximum temperature used is 86 degrees F. and the lowest minimumtemperature used is 50 degrees F. For each inbred or hybrid it takes acertain number of GDUs to reach various stages of plant development.

GDUSLK=GDU TO SILK: The number of growing degree units required for aninbred variety or hybrid to have approximately 50 percent of the plantswith silk emergence from time of planting. Growing degree units arecalculated by the Barger Method as given in GDU SHD definition and thendivided by 10.

GENE SILENCING: The interruption or suppression of the expression of agene at the level of transcription or translation.

GENOTYPE: Refers to the genetic mark-up or profile of a cell ororganism.

GIBERS=GIBBERELLA EAR ROT (PINK MOLD) (Gibberella zeae): A 1 to 9 visualrating indicating the resistance to Gibberella Ear Rot. A higher scoreindicates a higher resistance. Data are collected only when sufficientselection pressure exists in the experiment measured.

GIBROT=GIBBERELLA STALK ROT SCORE: Score of stalk rot severity due toGibberella (Gibberella zeae). Expressed as a 1 to 9 score with 9 beinghighly resistant. Data are collected only when sufficient selectionpressure exists in the experiment measured.

GLFSPT=GRAY LEAF SPOT (Cercospora zeae-maydis): A 1 to 9 visual ratingindicating the resistance to Gray Leaf Spot. A higher score indicates ahigher resistance. Data are collected only when sufficient selectionpressure exists in the experiment measured.

GOSWLT=GOSS' WILT (Corynebacterium nebraskense): A 1 to 9 visual ratingindicating the resistance to Goss' Wilt. A higher score indicates ahigher resistance. Data are collected only when sufficient selectionpressure exists in the experiment measured.

GRNAPP=GRAIN APPEARANCE: This is a 1 to 9 rating for the generalappearance of the shelled grain as it is harvested based on such factorsas the color of harvested grain, any mold on the grain, and any crackedgrain. High scores indicate good grain visual quality.

HAPLOID PLANT PART: Refers to a plant part or cell that has the samehaploid genotype as PH18K6.

H and H1: Refers to the haploid generation.

HCBLT=HELMINTHOSPORIUM CARBONUM LEAF BLIGHT (Helminthosporium carbonum):A 1 to 9 visual rating indicating the resistance to Helminthosporiuminfection. A higher score indicates a higher resistance. Data arecollected only when sufficient selection pressure exists in theexperiment measured.

HD SMT=HEAD SMUT (Sphacelotheca reiliana): This indicates the percentageof plants not infected. Data are collected only when sufficientselection pressure exists in the experiment measured.

HSKCVR=HUSK COVER: A 1 to 9 score based on performance relative to keychecks, with a score of 1 indicating very short husks, tip of ear andkernels showing; 5 is intermediate coverage of the ear under mostconditions, sometimes with thin husk; and a 9 has husks extending andclosed beyond the tip of the ear. Scoring can best be done nearphysiological maturity stage or any time during dry down untilharvested.

HTFRM=Near-infrared transmission spectroscopy, NIT, prediction offermentables.

HYBRID VARIETY: A substantially heterozygous hybrid line and minorgenetic modifications thereof that retain the overall genetics of thehybrid line including but not limited to a locus conversion, a mutation,or a somoclonal variant.

INBRED: A variety developed through inbreeding or doubled haploidy thatpreferably comprises homozygous alleles at about 95% or more of itsloci.

INC D/A=GROSS INCOME (DOLLARS PER ACRE): Relative income per acreassuming drying costs of two cents per point above 15.5 percent harvestmoisture and current market price per bushel.

INCOME/ACRE: Income advantage of hybrid to be patented over other hybridon per acre basis.

INC ADV=GROSS INCOME ADVANTAGE: Gross income advantage of variety #1over variety #2.

INTROGRESSION: The process of transferring genetic material from onegenotype to another.

KERUNT=KERNELS PER UNIT AREA (Acres or Hectares).

KERPOP=KERNEL POP SCORE: The visual 1-9 rating of the amount ofrupturing of the kernel pericarp at an early stage in grain fill. Ahigher score is good and indicates no popped (ruptured) kernels.

KER_WT=KERNEL NUMBER PER UNIT WEIGHT (Pounds or Kilograms): The numberof kernels in a specific measured weight; determined after removal ofextremely small and large kernels.

KSZDCD=KERNEL SIZE DISCARD: The percent of discard seed; calculated asthe sum of discarded tip kernels and extra large kernels.

LINKAGE: Refers to a phenomenon wherein alleles on the same chromosometend to segregate together more often than expected by chance if theirtransmission was independent.

LINKAGE DISEQUILIBRIUM: Refers to a phenomenon wherein alleles tend toremain together in linkage groups when segregating from parents tooffspring, with a greater frequency than expected from their individualfrequencies.

LOCUS: A specific location on a chromosome.

LOCUS CONVERSION: (Also called a TRAIT CONVERNSION) A locus conversionrefers to plants within a variety that have been modified in a mannerthat retains the overall genetics of the variety and further comprisesone or more loci with a specific desired trait, such as male sterility,insect control, disease control or herbicide tolerance. Examples ofsingle locus conversions include mutant genes, transgenes and nativetraits finely mapped to a single locus. One or more locus conversiontraits may be introduced into a single corn variety.

L/POP=YIELD AT LOW DENSITY: Yield ability at relatively low plantdensities on a 1 to 9 relative system with a higher number indicatingthe hybrid responds well to low plant densities for yield relative toother hybrids. A 1, 5, and 9 would represent very poor, average, andvery good yield response, respectively, to low plant density.

LRTLDG=LATE ROOT LODGING: The percentage of plants that do not rootlodge after anthesis through harvest; plants that lean from the verticalaxis at an approximately 30 degree angle or greater would be counted asroot lodged. Data are collected only when sufficient selection pressureexists in the experiment measured.

LRTLPN=LATE ROOT LODGING: An estimate of the percentage of plants thatdo not root lodge after anthesis through harvest; plants that lean fromthe vertical axis at an approximately 30 degree angle or greater wouldbe considered as root lodged. Data are collected only when sufficientselection pressure exists in the experiment measured.

LRTLSC=LATE ROOT LODGING SCORE: Score for severity of plants that leanfrom a vertical axis at an approximate 30 degree angle or greater whichtypically results from strong winds after flowering. Recorded prior toharvest when a root-lodging event has occurred. This lodging results inplants that are leaned or “lodged” over at the base of the plant and donot straighten or “goose-neck” back to a vertical position. Expressed asa 1 to 9 score with 9 being no lodging. Data are collected only whensufficient selection pressure exists in the experiment measured.

MALE STERILITY: A male sterile plant is one which produces no viablepollen no (pollen that is able to fertilize the egg to produce a viableseed). Male sterility prevents self pollination. These male sterileplants are therefore useful in hybrid plant production.

MDMCPX=MAIZE DWARF MOSAIC COMPLEX (MDMV=Maize Dwarf Mosaic Virus andMCDV=Maize Chlorotic Dwarf Virus). A 1 to 9 visual rating indicating theresistance to Maize Dwarf Mosaic Complex. A higher score indicates ahigher resistance. Data are collected only when sufficient selectionpressure exists in the experiment measured.

MILKLN=percent milk in mature grain.

MST=HARVEST MOISTURE: The moisture is the actual percentage moisture ofthe grain at harvest.

MSTADV=MOISTURE ADVANTAGE: The moisture advantage of variety #1 overvariety #2 as calculated by: MOISTURE of variety #2—MOISTURE of variety#1=MOISTURE ADVANTAGE of variety #1.

NEI DISTANCE: A quantitative measure of percent similarity between twovarieties. Nei's distance between varieties A and B can be defined as1-(2*number alleles in common/(number alleles in A+number alleles in B).For example, if varieties A and B are the same for 95 out of 100alleles, the Nei distance would be 0.05. If varieties A and B are thesame for 98 out of 100 alleles, the Nei distance would be 0.02. Freesoftware for calculating Nei distance is available on the internet atmultiple locations such as, for example, at:evolution.genetics.washington.edu/phylip.html. See Nei, Proc Natl AcadSci, 76:5269-5273 (1979) which is incorporated by reference for thispurpose.

NLFBLT=NORTHERN LEAF BLIGHT (Helminthosporium turcicum or Exserohilumturcicum): A 1 to 9 visual rating indicating the resistance to NorthernLeaf Blight. A higher score indicates a higher resistance. Data arecollected only when sufficient selection pressure exists in theexperiment measured.

NUCLEIC ACID: An acidic, chainlike biological macromolecule consistingof multiple repeat units of phosphoric acid, sugar and purine andpyrimidine bases.

OILT=GRAIN OIL: Absolute value of oil content of the kernel as predictedby Near-Infrared Transmittance and expressed as a percent of dry matter.

PERCENT IDENTITY: Percent identity as used herein refers to thecomparison of the alleles present in two varieties. For example, whencomparing two inbred plants to each other, each inbred plant will havethe same allele (and therefore be homozygous) at almost all of theirloci. Percent identity is determined by comparing a statisticallysignificant number of the homozygous alleles of two varieties. Forexample, a percent identity of 90% between PH18K6 and other varietymeans that the two varieties have the same homozygous alleles at 90% oftheir loci.

PLANT: As used herein, the term “plant” includes reference to animmature or mature whole plant, including a plant that has beendetasseled or from which seed or grain has been removed. Seed or embryothat will produce the plant is also considered to be the plant.

PLANT PART: As used herein, the term “plant part” includes leaves,stems, roots, seed, grain, embryo, pollen, ovules, flowers, ears, cobs,husks, stalks, root tips, anthers, pericarp, silk, tissue, cells and thelike.

PLATFORM indicates the variety with the base genetics and the varietywith the base genetics comprising locus conversion(s). There can be aplatform for the inbred maize variety and the hybrid maize variety.

PLTHT=PLANT HEIGHT: This is a measure of the height of the plant fromthe ground to the tip of the tassel in inches.

POLPRD=POLLEN PRODUCTION SCORE: The estimated total amount of pollenproduced by tassels based on the number of tassel branches and thedensity of the spikelets.

POLSC=POLLEN SCORE: A 1 to 9 visual rating indicating the amount ofpollen shed. The higher the score the more pollen shed.

POLWT=POLLEN WEIGHT: This is calculated by dry weight of tasselscollected as shedding commences minus dry weight from similar tasselsharvested after shedding is complete.

POP K/A=PLANT POPULATIONS: Measured as 1000's per acre.

POP ADV=PLANT POPULATION ADVANTAGE: The plant population advantage ofvariety #1 over variety #2 as calculated by PLANT POPULATION of variety#2—PLANT POPULATION of variety #1=PLANT POPULATION ADVANTAGE of variety#1.

PRM=PREDICTED RELATIVE MATURITY: This trait, predicted relativematurity, is based on the harvest moisture of the grain. The relativematurity rating is based on a known set of checks and utilizes standardlinear regression analyses and is also referred to as the ComparativeRelative Maturity Rating System that is similar to the MinnesotaRelative Maturity Rating System.

PRMSHD: A relative measure of the growing degree units (GDU) required toreach 50% pollen shed. Relative values are predicted values from thelinear regression of observed GDU's on relative maturity of commercialchecks.

PROT=GRAIN PROTEIN: Absolute value of protein content of the kernel aspredicted by Near-Infrared Transmittance and expressed as a percent ofdry matter.

RESISTANCE: Synonymous with tolerance. The ability of a plant towithstand exposure to an insect, disease, herbicide or other condition.A resistant plant variety will have a level of resistance higher than acomparable wild-type variety.

RTLDG=ROOT LODGING: Root lodging is the percentage of plants that do notroot lodge; plants that lean from the vertical axis at an approximately30 degree angle or greater would be counted as root lodged. Data arecollected only when sufficient selection pressure exists in theexperiment measured.

RTLADV=ROOT LODGING ADVANTAGE: The root lodging advantage of variety #1over variety #2. Data are collected only when sufficient selectionpressure exists in the experiment measured.

SCTGRN=SCATTER GRAIN: A 1 to 9 visual rating indicating the amount ofscatter grain (lack of pollination or kernel abortion) on the ear. Thehigher the score the less scatter grain.

SDGVGR=SEEDLING VIGOR: This is the visual rating (1 to 9) of the amountof vegetative growth after emergence at the seedling stage(approximately five leaves). A higher score indicates better vigor.

SEED: Fertilized and ripened ovule, consisting of the plant embryo,varying amounts of stored food material, and a protective outer seedcoat. Synonymous with grain.

SEFIELD: Percent stress emergence in field.

SELAB: Average % stress emergence in lab tests.

SEL IND=SELECTION INDEX: The selection index gives a single measure ofthe hybrid's worth based on information for multiple traits. A maizebreeder may utilize his or her own set of traits for the selectionindex. One of the traits that is almost always included is yield. Theselection index data presented in the tables represent the mean valueaveraged across testing stations.

SELF POLLINATION: A plant is self-pollinated if pollen from one floweris transferred to the same or another flower of the same plant.

SIB POLLINATION: A plant is sib-pollinated when individuals within thesame family or variety are used for pollination.

SITE SPECIFIC INTEGRATION: Genes that create a site for site specificDNA integration. This includes the introduction of FRT sites that may beused in the FLP/FRT system and/or Lox sites that may be used in theCre/Loxp system. For example, see Lyznik, et al., Site-SpecificRecombination for Genetic Engineering in Plants, Plant Cell Rep (2003)21:925-932 and WO 99/25821.

SLFBLT=SOUTHERN LEAF BLIGHT (Helminthosporium maydis or Bipolarismaydis): A 1 to 9 visual rating indicating the resistance to SouthernLeaf Blight. A higher score indicates a higher resistance. Data arecollected only when sufficient selection pressure exists in theexperiment measured.

SOURST=SOUTHERN RUST (Puccinia polysora): A 1 to 9 visual ratingindicating the resistance to Southern Rust. A higher score indicates ahigher resistance. Data are collected only when sufficient selectionpressure exists in the experiment measured.

SPKDSC=SPIKELET DENSITY SCORE: The visual 1-9 rating of how densespikelets are on the middle tassel branches. A higher score indicateshigher spikelet density.

STAGRN=STAY GREEN: Stay green is the measure of plant health near thetime of black layer formation (physiological maturity). A high scoreindicates better late-season plant health.

STDADV=STALK STANDING ADVANTAGE: The advantage of variety #1 overvariety #2 for the trait STKCNT.

STKCNT=NUMBER OF PLANTS: This is the final stand or number of plants perplot.

STKCTE: This is the early stand count of plants per plot.

STKLDG=STALK LODGING REGULAR: This is the percentage of plants that didnot stalk lodge (stalk breakage) at regular harvest (when grain moistureis between about 20% and 30%) as measured by either natural lodging orpushing the stalks and determining the percentage of plants that breakbelow the ear. Data are collected only when sufficient selectionpressure exists in the experiment measured.

STKLDS=STALK LODGING SCORE: A plant is considered as stalk lodged if thestalk is broken or crimped between the ear and the ground. This can becaused by any or a combination of the following: strong winds late inthe season, disease pressure within the stalks, ECB damage orgenetically weak stalks. This trait should be taken just prior to or atharvest. Expressed on a 1 to 9 scale with 9 being no lodging. Data arecollected only when sufficient selection pressure exists in theexperiment measured.

STLLPN=LATE STALK LODGING: This is the percent of plants that did notstalk lodge (stalk breakage or crimping) at or around late seasonharvest (when grain moisture is below 20%) as measured by either naturallodging or pushing the stalks and determining the percentage of plantsthat break or crimp below the ear. Data are collected only whensufficient selection pressure exists in the experiment measured.

STLPCN=STALK LODGING REGULAR: This is an estimate of the percentage ofplants that did not stalk lodge (stalk breakage) at regular harvest(when grain moisture is between about 20% and 30%) as measured by eithernatural lodging or pushing the stalks and determining the percentage ofplants that break below the ear. Data are collected only when sufficientselection pressure exists in the experiment measured.

STLTIP=STERILE TIPS SCORE: The visual 1 to 9 rating of the relative lackof glumes on the tassel central spike and branches. A higher scoreindicates less incidence of sterile tips or lack of glumes on thetassel.

STRT=GRAIN STARCH: Absolute value of starch content of the kernel aspredicted by Near-Infrared Transmittance and expressed as a percent ofdry matter.

STWWLT=Stewart's Wilt (Erwinia stewartii): A 1 to 9 visual ratingindicating the resistance to Stewart's Wilt. A higher score indicates ahigher resistance. Data are collected only when sufficient selectionpressure exists in the experiment measured.

SSRs: Genetic markers based on polymorphisms in repeated nucleotidesequences, such as microsatellites. A marker system based on SSRs can behighly informative in linkage analysis relative to other marker systemsin that multiple alleles may be present.

TASBLS=TASSEL BLAST: A 1 to 9 visual rating was used to measure thedegree of blasting (necrosis due to heat stress) of the tassel at thetime of flowering. A 1 would indicate a very high level of blasting attime of flowering, while a 9 would have no tassel blasting. Data arecollected only when sufficient selection pressure exists in theexperiment measured.

TASBRN=TASSEL BRANCH NUMBER: The number of tassel branches, with anthersoriginating from the central spike.

TASSZ=TASSEL SIZE: A 1 to 9 visual rating was used to indicate therelative size of the tassel. The higher the rating the larger thetassel.

TAS WT=TASSEL WEIGHT: This is the average weight of a tassel (grams)just prior to pollen shed.

TEXEAR=EAR TEXTURE: A 1 to 9 visual rating was used to indicate therelative hardness (smoothness of crown) of mature grain. A 1 would bevery soft (extreme dent) while a 9 would be very hard (flinty or verysmooth crown).

TILLER=TILLERS: A count of the number of tillers per plot that couldpossibly shed pollen was taken. Data are given as a percentage oftillers: number of tillers per plot divided by number of plants perplot. A tiller is defined as a secondary shoot that has developed as atassel capable of shedding pollen.

TSTWTN=TEST WEIGHT (ADJUSTED): The measure of the weight of the grain(in pounds) for a given volume (bushel), adjusted for MST less than orequal to 22%.

TSTWTN=TEST WEIGHT (UNADJUSTED): The measure of the weight of the grainin pounds for a given volume (bushel).

TSWADV=TEST WEIGHT ADVANTAGE: The test weight advantage of variety #1over variety #2.

VARIETY: A maize line and minor genetic modifications thereof thatretain the overall genetics of the line including but not limited to alocus conversion, a mutation, or a somoclonal variant.

WIN M %=PERCENT MOISTURE WINS.

WIN Y %=PERCENT YIELD WINS.

YIELD BU/A=YIELD (BUSHELS/ACRE): Yield of the grain at harvest by weightor volume (bushels) per unit area (acre) adjusted to 15% moisture.

YLDADV=YIELD ADVANTAGE: The yield advantage of variety #1 over variety#2 as calculated by: YIELD of variety #1−YIELD variety #2=YIELDADVANTAGE of variety #1.

YIELDMST=YIELD/MOISTURE RATIO.

YLDSC=YIELD SCORE: A 1 to 9 visual rating was used to give a relativerating for yield based on plot ear piles. The higher the rating thegreater visual yield appearance.

DETAILED DESCRIPTION OF THE INVENTION AND FURTHER EMBODIMENTS

All tables discussed in the Detailed Description of the Invention andFurther Embodiments section can found at the end of the section.

Breeding History of PH18K6

Inbred Maize variety PH18K6 was developed by the following method. Across was made between inbred line PHE3D and inbred line PHE4N. InbredPH18K6 was developed by selfing the F1 plants, selfing and bulking theF2, selfing and using ear-to-row (pedigree) selection from the F3 to F8generation, and bulking the F9 seed.

Maize variety PH18K6, being substantially homozygous, can be reproducedby planting seeds of the variety, growing the resulting maize plantsunder self-pollinating or sib-pollinating conditions with adequateisolation, and harvesting the resulting seed using techniques familiarto the agricultural arts.

Phenotypic Characteristics of PH18K6

Inbred maize variety PH18K6 may be used as a male or female in theproduction of the first generation F1 hybrid. Inbred maize varietyPH18K6 has a relative maturity of approximately 105 based on theComparative Relative Maturity Rating System for harvest moisture ofgrain. The variety has shown uniformity and stability within the limitsof environmental influence for all the traits as described in theVariety Description Information (Table 1, found at the end of thesection). The variety has been self-pollinated and ear-rowed asufficient number of generations with careful attention paid touniformity of plant type to ensure the homozygosity and phenotypicstability necessary for use in commercial hybrid seed production. Thevariety has been increased both by hand and in isolated fields withcontinued observation for uniformity. No variant traits have beenobserved or are expected in PH18K6.

Genotypic Characteristics of PH18K6

In addition to phenotypic observations, a plant can also be identifiedby its genotype. The genotype of a plant can be characterized through agenetic marker profile.

As a result of inbreeding, PH18K6 is substantially homozygous. Thishomozygosity can be characterized at the loci shown in a marker profile.An F1 hybrid made with PH18K6 would substantially comprise the markerprofile of PH18K6. This is because an F1 hybrid is the sum of its inbredparents, e.g., if one inbred parent is homozygous for allele x at aparticular locus, and the other inbred parent is homozygous for allele yat that locus, the F1 hybrid will be x.y (heterozygous) at that locus. Agenetic marker profile can therefore be used to identify hybridscomprising PH18K6 as a parent, since such hybrids will comprise two setsof alleles, one set of which will be from PH18K6. The determination ofthe male set of alleles and the female set of alleles may be made byprofiling the hybrid and the pericarp of the hybrid seed, which iscomposed of maternal parent cells. One way to obtain the paternal parentprofile is to subtract the pericarp profile from the hybrid profile.

Subsequent generations of progeny produced by selection and breeding areexpected to be of genotype xx (homozygous), yy (homozygous), or xy(heterozygous) for these locus positions. When the F1 plant is used toproduce an inbred, the resulting inbred should be either x or y for thatallele.

Therefore, in accordance with the above, an embodiment of this inventionis a PH18K6 progeny maize plant or plant part that is a first generation(F1) hybrid maize plant comprising two sets of alleles, wherein one setof the alleles is the same as PH18K6 at substantially all loci. A maizecell wherein one set of the alleles is the same as PH18K6 atsubstantially all loci is also an embodiment of the invention. Thismaize cell may be a part of a hybrid seed, plant or plant part producedby crossing PH18K6 with another maize plant.

Genetic marker profiles can be obtained by techniques such asRestriction Fragment Length Polymorphisms (RFLPs), Randomly AmplifiedPolymorphic DNAs (RAPDs), Arbitrarily Primed Polymerase Chain Reaction(AP-PCR), DNA Amplification Fingerprinting (DAF), Sequence CharacterizedAmplified Regions (SCARs), Amplified Fragment Length Polymorphisms(AFLPs), Simple Sequence Repeats (SSRs) which are also referred to asMicrosatellites, and Single Nucleotide Polymorphisms (SNPs). Forexample, see Berry, Don et al., “Assessing Probability of Ancestry UsingSimple Sequence Repeat Profiles: Applications to Maize Hybrids andInbreds”, Genetics, 2002, 161:813-824, and Berry, Don et al., “AssessingProbability of Ancestry Using Simple Sequence Repeat Profiles:Applications to Maize Inbred Lines and Soybean Varieties”, Genetics,2003, 165: 331-342.

Particular markers used for these purposes are not limited to the set ofmarkers disclosed herein, but may include any type of marker and markerprofile which provides a means of distinguishing varieties. In additionto being used for identification of maize variety PH18K6, a hybridproduced through the use of PH18K6, and the identification orverification of pedigree for progeny plants produced through the use ofPH18K6, a genetic marker profile is also useful in developing a locusconversion of PH18K6.

Means of performing genetic marker profiles using SSR polymorphisms arewell known in the art. SSRs are genetic markers based on polymorphismsin repeated nucleotide sequences, such as microsatellites. A markersystem based on SSRs can be highly informative in linkage analysisrelative to other marker systems in that multiple alleles may bepresent. Another advantage of this type of marker is that, through useof flanking primers, detection of SSRs can be achieved, for example, bythe polymerase chain reaction (PCR), thereby eliminating the need forlabor-intensive Southern hybridization. The PCR detection is done by useof two oligonucleotide primers flanking the polymorphic segment ofrepetitive DNA. Repeated cycles of heat denaturation of the DNA followedby annealing of the primers to their complementary sequences at lowtemperatures, and extension of the annealed primers with DNA polymerase,comprise the major part of the methodology.

Following amplification, markers can be scored by electrophoresis of theamplification products. Scoring of marker genotype is based on the sizeof the amplified fragment, which may be measured by the number of basepairs of the fragment. While variation in the primer used or inlaboratory procedures can affect the reported fragment size, relativevalues should remain constant regardless of the specific primer orlaboratory used. When comparing plants it is preferable if all SSRprofiles are performed in the same lab. An SSR service is available tothe public on a contractual basis by DNA Landmarks inSaint-Jean-sur-Richelieu, Quebec, Canada.

Primers used to perform SSRs are publicly available and may be found inthe Maize GDB on the World Wide Web at maizegdb.org (sponsored by theUSDA Agricultural Research Service), in Sharopova et al. (Plant Mol.Biol. 48(5-6):463-481), Lee et al. (Plant Mol. Biol. 48(5-6); 453-461).Primers may be constructed from publicly available sequence information.Some marker information may also be available from DNA Landmarks.

PH18K6 and its plant parts can be identified through a molecular markerprofile. Such plant parts may be either diploid or haploid. Alsoencompassed within the scope of the invention are plants and plant partssubstantially benefiting from the use of PH18K6 in their development,such as PH18K6 comprising a locus conversion.

Comparing PH18K6 to Other Inbreds

A breeder uses various methods to help determine which plants should beselected from segregating populations and ultimately which inbredvarieties will be used to develop hybrids for commercialization. Inaddition to knowledge of the germplasm and plant genetics, a part of theselection process is dependent on experimental design coupled with theuse of statistical analysis. Experimental design and statisticalanalysis are used to help determine which plants, which family ofplants, and finally which inbred varieties and hybrid combinations aresignificantly better or different for one or more traits of interest.Experimental design methods are used to assess error so that differencesbetween two inbred varieties or two hybrid varieties can be moreaccurately evaluated. Statistical analysis includes the calculation ofmean values, determination of the statistical significance of thesources of variation, and the calculation of the appropriate variancecomponents. Either a five or a one percent significance level iscustomarily used to determine whether a difference that occurs for agiven trait is real or due to the environment or experimental error. Oneof ordinary skill in the art of plant breeding would know how toevaluate the traits of two plant varieties to determine if there is asignificant difference between the two traits expressed by thosevarieties. For example, see Fehr, Walt, Principles of CultivarDevelopment, p. 261-286 (1987). Mean trait values may be used todetermine whether trait differences are significant. Trait values shouldpreferably be measured on plants grown under the same environmentalconditions, and environmental conditions should be appropriate for thetraits or traits being evaluated. Sufficient selection pressure shouldbe present for optimum measurement of traits of interest such asherbicide tolerance, insect or disease resistance. A locus conversion ofPH18K6 for herbicide tolerance should be compared with an isogeniccounterpart in the absence of the converted trait. In addition, a locusconversion for insect or disease resistance should be compared to theisogenic counterpart, in the absence of disease pressure or insectpressure.

Development of Maize Hybrids Using PH18K6

A single cross maize hybrid results from the cross of two inbredvarieties, each of which has a genotype that complements the genotype ofthe other. A hybrid progeny of the first generation is designated F1. Inthe development of commercial hybrids in a maize plant breeding program,only the F1 hybrid plants are sought. F1 hybrids are more vigorous thantheir inbred parents. This hybrid vigor, or heterosis, can be manifestedin many polygenic traits, including increased vegetative growth andincreased yield.

PH18K6 may be used to produce hybrid maize. One such embodiment is themethod of crossing maize variety PH18K6 with another maize plant, suchas a different maize variety, to form a first generation F1 hybrid seed.The first generation F1 hybrid seed, plant and plant part produced bythis method is an embodiment of the invention. The first generation F1seed, plant and plant part will comprise an essentially complete set ofthe alleles of variety PH18K6. One of ordinary skill in the art canutilize molecular methods to identify a particular F1 hybrid plantproduced using variety PH18K6. Further, one of ordinary skill in the artmay also produce F1 hybrids with transgenic, male sterile and/or locusconversions of variety PH18K6.

The development of a maize hybrid in a maize plant breeding programinvolves three steps: (1) the selection of plants from various germplasmpools for initial breeding crosses; (2) the selfing of the selectedplants from the breeding crosses for several generations to produce aseries of varieties, such as PH18K6, which, although different from eachother, breed true and are highly uniform; and (3) crossing the selectedvarieties with different varieties to produce the hybrids. During theinbreeding process in maize, the vigor of the varieties decreases, andso one would not be likely to use PH18K6 directly to produce grain.However, vigor is restored when PH18K6 is crossed to a different inbredvariety to produce a commercial F1 hybrid. An important consequence ofthe homozygosity and homogeneity of the inbred variety is that thehybrid between a defined pair of inbreds may be reproduced indefinitelyas long as the homogeneity of the inbred parents is maintained.

PH18K6 may be used to produce a single cross hybrid, a double crosshybrid, or a three-way hybrid. A single cross hybrid is produced whentwo inbred varieties are crossed to produce the F1 progeny. A doublecross hybrid is produced from four inbred varieties crossed in pairs(A×B and C×D) and then the two F1 hybrids are crossed again (A×B)×(C×D).A three-way cross hybrid is produced from three inbred varieties wheretwo of the inbred varieties are crossed (A×B) and then the resulting F1hybrid is crossed with the third inbred (A×B)×C. In each case, pericarptissue from the female parent will be a part of and protect the hybridseed.

Combining Ability of PH18K6

Combining ability of a variety, as well as the performance of thevariety per se, is a factor in the selection of improved maize inbreds.Combining ability refers to a variety's contribution as a parent whencrossed with other varieties to form hybrids. The hybrids formed for thepurpose of selecting superior varieties may be referred to as testcrosses, and include comparisons to other hybrid varieties grown in thesame environment (same cross, location and time of planting). One way ofmeasuring combining ability is by using values based in part on theoverall mean of a number of test crosses weighted by number ofexperiment and location combinations in which the hybrid combinationsoccurs. The mean may be adjusted to remove environmental effects andknown genetic relationships among the varieties.

General combining ability provides an overall score for the inbred overa large number of test crosses. Specific combining ability providesinformation on hybrid combinations formed by PH18K6 and a specificinbred parent. A variety such as PH18K6 which exhibits good generalcombining ability may be used in a large number of hybrid combinations.

A general combining ability report for PH18K6 is provided in Table 2. InTable 2, found at the end of this section, BLUP, Best Linear UnbiasedPrediction, values are reported for the breeding value of the maizeinbred PH18K6 platform. The BLUP values are reported for numerous traitsof hybrids that have inbred PH18K6 or a locus conversion of PH18K6 as aparent. The inbred PH18K6 and various locus conversions of PH18K6 aretogether considered a platform. The values reported indicate a BLUPvalue averaged for all members of the platform weighted by the inverseof the Standard Errors.

Hybrid Comparisons

These hybrid comparisons represent specific hybrid crosses with PH18K6and a comparison of these specific hybrids with other hybrids withfavorable characteristics. These comparisons illustrate the goodspecific combining ability of PH18K6.

The results in Table 3 compare a specific hybrid for which PH18K6 is aparent with other hybrids. The data in Table 3 shows that numerousspecies of the genus of F1 hybrids created with PH18K6 have been reducedto practice. These comparisons illustrate the good specific combiningability of PH18K6. In Table 3, found at the end of this section, BLUPvalues are reported for different hybrids wherein one parent is themaize variety PH18K6 or PH18K6 comprising locus conversions. The BLUPvalues and Standard Errors, SE, are reported for numerous traits.

Data are presented for these hybrids are based on replicated fieldtrials.

Locus Conversions of PH18K6

PH18K6 represents a new base genetic variety into which a new locus maybe introgressed. Direct transformation and backcrossing represent twoimportant methods that can be used to accomplish such an introgression.The term locus conversion is used to designate the product of such anintrogression.

A locus conversion of PH18K6 will retain the genetic integrity ofPH18K6. A locus conversion of PH18K6 will comprise at least 90%, 91%,92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% of the genetic identity ofPH18K6 as determined by using SSR markers or SNP markers. For example, alocus conversion of PH18K6 can be developed when DNA sequences areintroduced through backcrossing (Hallauer et al. in Corn and CornImprovement, Sprague and Dudley, Third Ed. 1998), with PH18K6 utilizedas the recurrent parent. Both naturally occurring and transgenic DNAsequences may be introduced through backcrossing techniques. A backcrossconversion may produce a plant with a trait or locus conversion in atleast one or more backcrosses, including at least 2 crosses, at least 3crosses, at least 4 crosses, at least 5 crosses and the like. Molecularmarker assisted breeding or selection may be utilized to reduce thenumber of backcrosses necessary to achieve the backcross conversion. Forexample, see Openshaw, S. J. et al., Marker-assisted Selection inBackcross Breeding, In: Proceedings Symposium of the Analysis ofMolecular Data, August 1994, Crop Science Society of America, Corvallis,Oreg., where it is demonstrated that a locus conversion can be made inas few as two backcrosses.

The complexity of the backcross conversion method depends on the type oftrait being transferred (single genes or closely linked genes as vs.unlinked genes), the level of expression of the trait, the type ofinheritance (cytoplasmic or nuclear) and the types of parents includedin the cross. It is understood by those of ordinary skill in the artthat for single locus traits that are relatively easy to classify, thebackcross method is effective and relatively easy to manage. (SeeHallauer et al. in Corn and Corn Improvement, Sprague and Dudley, ThirdEd. 1998). Desired traits that may be transferred through locusconversion include, but are not limited to, waxy starch, sterility(nuclear and cytoplasmic), fertility restoration, grain color (white),nutritional enhancements, drought resistance, enhanced nitrogenutilization efficiency, altered nitrogen responsiveness, altered fattyacid profile, increased digestibility, low phytate, industrialenhancements, disease resistance (bacterial, fungal or viral), insectresistance, herbicide tolerance and yield enhancements. A locusconversion, also called a trait conversion, can be a native trait or atransgenic trait. In addition, an introgression site itself, such as anFRT site, Lox site or other site specific integration site, may beinserted by backcrossing and utilized for direct insertion of one ormore genes of interest into a specific plant variety. The seed industrycommonly markets “triple stacks” of base genetics; which can bevarieties comprising a locus conversion of at least 3 loci. Similarly,“quadruple stacks” would comprise the base genetics and could comprise alocus conversion of at least 4 loci. A single locus may contain severaltransgenes, such as a transgene for disease resistance that, in the sameexpression vector, also contains a transgene for herbicide tolerance. Asused herein, the phrase ‘comprising a’ transgene, transgenic event orlocus conversion means one or more transgenes, transgenic events orlocus conversions. The gene for herbicide tolerance may be used as aselectable marker and/or as a phenotypic trait. A locus conversion of asite specific integration system allows for the integration of multiplegenes at the converted loci. Further, SSI and FRT technologies known tothose of skill in the art in the art may result in multiple geneintrogressions at a single locus.

The locus conversion may result from either the transfer of a dominantallele or a recessive allele. Selection of progeny containing the traitof interest is accomplished by direct selection for a trait associatedwith a dominant allele. Transgenes transferred via backcrossingtypically function as a dominant single gene trait and are relativelyeasy to classify. Selection of progeny for a trait that is transferredvia a recessive allele, such as the waxy starch characteristic, requiresgrowing and selfing the first backcross generation to determine whichplants carry the recessive alleles. Recessive traits may requireadditional progeny testing in successive backcross generations todetermine the presence of the locus of interest. The last backcrossgeneration is usually selfed to give pure breeding progeny for thegene(s) being transferred, although a backcross conversion with a stablyintrogressed trait may also be maintained by further backcrossing to therecurrent parent with selection for the converted trait.

Along with selection for the trait of interest, progeny are selected forthe phenotype and/or genotype of the recurrent parent. Whileoccasionally additional polynucleotide sequences or genes may betransferred along with the backcross conversion, the backcrossconversion variety “fits into the same hybrid combination as therecurrent parent inbred variety and contributes the effect of theadditional locus added through the backcross.” ((Poehlman et al (1995)Breeding Field Crop, 4th Ed., Iowa State University Press, Ames, Iowa.,pp. 132-155 and 321-344)). When one or more traits are introgressed intothe variety a difference in quantitative agronomic traits, such as yieldor dry down, between the variety and an introgressed version of thevariety in some environments may occur. For example, the introgressedversion may provide a net yield increase in environments where the traitprovides a benefit, such as when a variety with an introgressed traitfor insect resistance is grown in an environment where insect pressureexists, or when a variety with herbicide tolerance is grown in anenvironment where herbicide is used.

One process for adding or modifying a trait or locus in maize varietyPH18K6 comprises crossing PH18K6 plants grown from PH18K6 seed withplants of another maize variety that comprise the desired trait orlocus, selecting F1 progeny plants that comprise the desired trait orlocus to produce selected F1 progeny plants, crossing the selectedprogeny plants with the PH18K6 plants to produce backcross progenyplants, selecting for backcross progeny plants that have the desiredtrait or locus and the phenotypic characteristics of maize varietyPH18K6 to produce selected backcross progeny plants; and backcrossing toPH18K6 one or more times in succession to produce backcross progenyplants that comprise said trait or locus. The modified PH18K6 may befurther characterized as having essentially the same phenotypiccharacteristics of maize variety PH18K6 listed in Table 1 and/or may becharacterized by percent identity to PH18K6 as determined by molecularmarkers, such as SSR markers or SNPs.

In addition, the above process and other similar processes describedherein may be used to produce F1 hybrid maize seed by adding a step atthe end of the process that comprises crossing PH18K6 with the locusconversion with a different maize plant and harvesting the resultant F1hybrid maize seed.

Traits are also used by those of ordinary skill in the art tocharacterize progeny. Traits are commonly evaluated at a significancelevel, such as a 1%, 5% or 10% significance level, when measured inplants grown in the same environmental conditions.

Male Sterility and Hybrid Seed Production

Hybrid seed production requires elimination or inactivation of pollenproduced by the female inbred parent. Incomplete removal or inactivationof the pollen provides the potential for self-pollination. A reliablemethod of controlling male fertility in plants offers the opportunityfor improved seed production.

PH18K6 can be produced in a male-sterile form. There are several ways inwhich a maize plant can be manipulated so that it is male sterile. Theseinclude use of manual or mechanical emasculation (or detasseling), useof one or more genetic factors that confer male sterility, includingcytoplasmic genetic and/or nuclear genetic male sterility, use ofgametocides and the like. A male sterile designated PH18K6 may includeone or more genetic factors, which result in cytoplasmic genetic and/ornuclear genetic male sterility. All of such embodiments are within thescope of the present claims. The male sterility may be either partial orcomplete male sterility.

Hybrid maize seed is often produced by a male sterility systemincorporating manual or mechanical detasseling. Alternate strips of twomaize inbreds are planted in a field, and the pollen-bearing tassels areremoved from one of the inbreds (female). Provided that there issufficient isolation from sources of foreign maize pollen, the ears ofthe detasseled inbred will be fertilized only from the other inbred(male), and the resulting seed is therefore hybrid and will form hybridplants.

The laborious detasseling process can be avoided by using cytoplasmicmale-sterile (CMS) inbreds. Plants of a CMS inbred are male sterile as aresult of genetic factors in the cytoplasm, as opposed to the nucleus,and so nuclear linked genes are not transferred during backcrossing.Thus, this characteristic is inherited exclusively through the femaleparent in maize plants, since only the female provides cytoplasm to thefertilized seed. CMS plants are fertilized with pollen from anotherinbred that is not male-sterile. Pollen from the second inbred may ormay not contribute genes that make the hybrid plants male-fertile, andeither option may be preferred depending on the intended use of thehybrid. The same hybrid seed, a portion produced from detasseled fertilemaize and a portion produced using the CMS system, can be blended toinsure that adequate pollen loads are available for fertilization whenthe hybrid plants are grown. CMS systems have been successfully usedsince the 1950's, and the male sterility trait is routinely backcrossedinto inbred varieties. See Wych, Robert D. (1988) “Production of HybridSeed”, Corn and Corn Improvement, Ch. 9, pp. 565-607.

There are several methods of conferring genetic male sterilityavailable, such as multiple mutant genes at separate locations withinthe genome that confer male sterility, as disclosed in U.S. Pat. Nos.4,654,465 and 4,727,219 to Brar et al. and chromosomal translocations asdescribed by Patterson in U.S. Pat. Nos. 3,861,709 and 3,710,511. Inaddition to these methods, Albertsen et al., U.S. Pat. No. 5,432,068,describes a system of nuclear male sterility which includes: identifyinga gene which is critical to male fertility; silencing this native genewhich is critical to male fertility; removing the native promoter fromthe essential male fertility gene and replacing it with an induciblepromoter; inserting this genetically engineered gene back into theplant; and thus creating a plant that is male sterile because theinducible promoter is not “on” resulting in the male fertility gene notbeing transcribed. Fertility is restored by inducing, or turning “on”,the promoter, which in turn allows the gene that confers male fertilityto be transcribed.

These, and the other methods of conferring genetic male sterility in theart, each possess their own benefits and drawbacks. Some other methodsuse a variety of approaches such as delivering into the plant a geneencoding a cytotoxic substance associated with a male tissue specificpromoter or an antisense system in which a gene critical to fertility isidentified and an antisense to that gene is inserted in the plant (seeFabinjanski, et al. EPO 89/3010153.8 publication no. 329,308 and PCTapplication PCT/CA90/00037 published as WO 90/08828).

Another system for controlling male sterility makes use of gametocides.Gametocides are not a genetic system, but rather a topical applicationof chemicals. These chemicals affect cells that are critical to malefertility. The application of these chemicals affects fertility in theplants only for the growing season in which the gametocide is applied(see Carlson, Glenn R., and U.S. Pat. No. 4,936,904). Application of thegametocide, timing of the application and genotype specificity oftenlimit the usefulness of the approach and it is not appropriate in allsituations.

Incomplete control over male fertility may result in self-pollinatedseed being unintentionally harvested and packaged with hybrid seed. Thiswould typically be only female parent seed, because the male plant isgrown in rows that are typically destroyed prior to seed development.Once the seed from the hybrid bag is planted, it is possible to identifyand select these self-pollinated plants. These self-pollinated plantswill be one of the inbred varieties used to produce the hybrid. Thoughthe possibility of PH18K6 being included in a hybrid seed bag exists,the occurrence is very low because much care is taken by seed companiesto avoid such inclusions. It is worth noting that hybrid seed is sold togrowers for the production of grain or forage and not for breeding orseed production. These self-pollinated plants can be identified andselected by one skilled in the art due to their less vigorous appearancefor vegetative and/or reproductive characteristics, including shorterplant height, small ear size, ear and kernel shape, or othercharacteristics.

Identification of these self-pollinated varieties can also beaccomplished through molecular marker analyses. See, “The Identificationof Female Selfs in Hybrid Maize: A Comparison Using Electrophoresis andMorphology”, Smith, J. S. C. and Wych, R. D., Seed Science andTechnology 14, 1-8 (1995), the disclosure of which is expresslyincorporated herein by reference. Through these technologies, thehomozygosity of the self pollinated variety can be verified by analyzingallelic composition at various loci along the genome. Those methodsallow for rapid identification of the invention disclosed herein. Seealso, “Identification of Atypical Plants in Hybrid Maize Seed byPostcontrol and Electrophoresis” Sarca, V. et al., Probleme de GeneticaTeoritica si Aplicata Vol. 20 (1) p. 29-42.

Transformation

The advent of new molecular biological techniques has allowed theisolation and characterization of genetic elements with specificfunctions, such as encoding specific protein products. Scientists in thefield of plant biology developed a strong interest in engineering thegenome of plants to contain and express foreign genetic elements, oradditional, or modified versions of native or endogenous geneticelements in order to alter the traits of a plant in a specific manner.Any DNA sequences, whether from a different species or from the samespecies, which are stably inserted into the cell using transformationare referred to herein collectively as “transgenes” and/or “transgenicevents”. In some embodiments of the invention, a transformed variant ofPH18K6 may comprise at least one transgene but could contain at least 1,2, 3, 4, 5, 6, 7, 8, 9, 10 and/or no more than 15, 14, 13, 12, 11, 10,9, 8, 7, 6, 5, 4, 3, or 2. Over the last fifteen to twenty years severalmethods for producing transgenic plants have been developed, and thepresent invention also relates to transformed versions of the claimedmaize variety PH18K6 as well as hybrid combinations thereof.

Numerous methods for plant transformation have been developed, includingbiological and physical plant transformation protocols. See, forexample, Miki et al., “Procedures for Introducing Foreign DNA intoPlants” in Methods in Plant Molecular Biology and Biotechnology, Glick,B. R. and Thompson, J. E. Eds. (CRC Press, Inc., Boca Raton, 1993) pages67-88 and Armstrong, “The First Decade of Maize Transformation: A Reviewand Future Perspective” (Maydica 44:101-109, 1999). In addition,expression vectors and in vitro culture methods for plant cell or tissuetransformation and regeneration of plants are available. See, forexample, Gruber et al., “Vectors for Plant Transformation” in Methods inPlant Molecular Biology and Biotechnology, Glick, B. R. and Thompson, J.E. Eds. (CRC Press, Inc., Boca Raton, 1993) pages 89-119.

The most prevalent types of plant transformation involve theconstruction of an expression vector. Such a vector comprises a DNAsequence that contains a gene under the control of or operatively linkedto a regulatory element, for example a promoter. The vector may containone or more genes and one or more regulatory elements.

A transgenic event which has been stably engineered into the germ cellline of a particular maize plant using transformation techniques, couldbe moved into the germ cell line of another variety using traditionalbreeding techniques that are well known in the plant breeding arts. Forexample, a backcrossing approach is commonly used to move a transgenicevent from a transformed maize plant to another variety, and theresulting progeny would then comprise the transgenic event(s). Also, ifan inbred variety was used for the transformation then the transgenicplants could be crossed to a different inbred in order to produce atransgenic hybrid maize plant.

Various genetic elements can be introduced into the plant genome usingtransformation. These elements include, but are not limited to genes;coding sequences; inducible, constitutive, and tissue specificpromoters; enhancing sequences; and signal and targeting sequences. Forexample, see the traits, genes and transformation methods listed in U.S.Pat. Nos. 6,118,055 and 6,284,953, which are herein incorporated byreference. In addition, transformability of a variety can be increasedby introgressing the trait of high transformability from another varietyknown to have high transformability, such as Hi-II. See U.S. PatentApplication Publication US200410016030 (2004).

With transgenic plants according to the present invention, a foreignprotein can be produced in commercial quantities. Thus, techniques forthe selection and propagation of transformed plants, which are wellunderstood in the art, yield a plurality of transgenic plants that areharvested in a conventional manner, and a foreign protein then can beextracted from a tissue of interest or from total biomass. Proteinextraction from plant biomass can be accomplished by known methods whichare discussed, for example, by Heney and Orr, Anal. Biochem. 114: 92-6(1981).

Transgenic events can be mapped by one of ordinary skill in the art andsuch techniques are well known to those of ordinary skill in the art.For exemplary methodologies in this regard, see for example, Glick andThompson, Methods in Plant Molecular Biology and Biotechnology 269-284(CRC Press, Boca Raton, 1993).

Likewise, by means of the present invention, plants can be geneticallyengineered to express various phenotypes of agronomic interest. Throughthe transformation of maize the expression of genes can be altered toenhance disease resistance, insect resistance, herbicide tolerance,agronomic traits, grain quality and other traits. Transformation canalso be used to insert DNA sequences which control or help controlmale-sterility. DNA sequences native to maize as well as non-native DNAsequences can be transformed into maize and used to alter levels ofnative or non-native proteins. Various promoters, targeting sequences,enhancing sequences, and other DNA sequences can be inserted into themaize genome for the purpose of altering the expression of proteins.Reduction of the activity of specific genes (also known as genesilencing, or gene suppression) is desirable for several aspects ofgenetic engineering in plants.

Many techniques for gene silencing are well known to one of skill in theart, including but not limited to knock-outs (such as by insertion of atransposable element such as mu (Vicki Chandler, The Maize Handbook Ch.118 (Springer-Verlag 1994) or other genetic elements such as a FRT, Loxor other site specific integration site, antisense technology (see,e.g., Sheehy et al. (1988) PNAS USA 85:8805-8809; and U.S. Pat. Nos.5,107,065; 5,453,566; and 5,759,829); co-suppression (e.g., Taylor(1997) Plant Cell 9:1245; Jorgensen (1990) Trends Biotech.8(12):340-344; Flavell (1994) PNAS USA 91:3490-3496; Finnegan et al.(1994) Bio/Technology 12: 883-888; and Neuhuber et al. (1994) Mol. Gen.Genet. 244:230-241); RNA interference (Napoli et al. (1990) Plant Cell2:279-289; U.S. Pat. No. 5,034,323; Sharp (1999) Genes Dev. 13:139-141;Zamore et al. (2000) Cell 101:25-33; and Montgomery et al. (1998) PNASUSA 95:15502-15507), virus-induced gene silencing (Burton, et al. (2000)Plant Cell 12:691-705; and Baulcombe (1999) Curr. Op. Plant Bio.2:109-113); target-RNA-specific ribozymes (Haseloff et al. (1988) Nature334: 585-591); hairpin structures (Smith et al. (2000) Nature407:319-320; WO 99/53050; and WO 98/53083); MicroRNA (Aukerman & Sakai(2003) Plant Cell 15:2730-2741); ribozymes (Steinecke et al. (1992) EMBOJ. 11:1525; and Perriman et al. (1993) Antisense Res. Dev. 3:253);oligonucleotide mediated targeted modification (e.g., WO 03/076574 andWO 99/25853); Zn-finger targeted molecules (e.g., WO 01/52620; WO03/048345; and WO 00/42219); and other methods or combinations of theabove methods known to those of skill in the art.

Exemplary nucleotide sequences that may be altered by geneticengineering include, but are not limited to, those categorized below.

1. Transgenes that Confer Resistance to Insects or Disease and thatEncode:

(A) Plant disease resistance genes. Plant defenses are often activatedby specific interaction between the product of a disease resistance gene(R) in the plant and the product of a corresponding avirulence (Avr)gene in the pathogen. A plant variety can be transformed with clonedresistance gene to engineer plants that are resistant to specificpathogen strains. See, for example Jones et al., Science 266: 789 (1994)(cloning of the tomato Cf-9 gene for resistance to Cladosporium fulvum);Martin et al., Science 262: 1432 (1993) (tomato Pto gene for resistanceto Pseudomonas syringae pv. tomato encodes a protein kinase); Mindrinoset al., Cell 78: 1089 (1994) (Arabidopsis RSP2 gene for resistance toPseudomonas syringae), McDowell & Woffenden, (2003) Trends Biotechnol.21(4): 178-83 and Toyoda et al., (2002) Transgenic Res. 11(6):567-82. Aplant resistant to a disease is one that is more resistant to a pathogenas compared to the wild type plant.

(B) A Bacillus thuringiensis protein, a derivative thereof or asynthetic polypeptide modeled thereon. See, for example, Geiser et al.,Gene 48: 109 (1986), who disclose the cloning and nucleotide sequence ofa Bt delta-endotoxin gene. Moreover, DNA molecules encodingdelta-endotoxin genes can be purchased from American Type CultureCollection (Rockville, Md.), for example, under ATCC Accession Nos.40098, 67136, 31995 and 31998. Other non-limiting examples of Bacillusthuringiensis transgenes being genetically engineered are given in thefollowing patents and patent applications and hereby are incorporated byreference for this purpose: U.S. Pat. Nos. 5,188,960; 5,689,052;5,880,275; 5,986,177; 7,105,332; 7,208,474; WO 91/14778; WO 99/31248; WO01/12731; WO 99/24581; WO 97/40162 and U.S. application Ser. Nos.10/032,717; 10/414,637; 11/018,615; 11/404,297; 11/404,638; 11/471,878;11/780,501; 11/780,511; 11/780,503; 11/953,648; 11/953,648; and11/957,893.

(C) An insect-specific hormone or pheromone such as an ecdysteroid andjuvenile hormone, a variant thereof, a mimetic based thereon, or anantagonist or agonist thereof. See, for example, the disclosure byHammock et al., Nature 344: 458 (1990), of baculovirus expression ofcloned juvenile hormone esterase, an inactivator of juvenile hormone.

(D) An insect-specific peptide which, upon expression, disrupts thephysiology of the affected pest. For example, see the disclosures ofRegan, J. Biol. Chem. 269: 9 (1994) (expression cloning yields DNAcoding for insect diuretic hormone receptor); Pratt et al., Biochem.Biophys. Res. Comm. 163: 1243 (1989) (an allostatin is identified inDiploptera puntata); Chattopadhyay et al. (2004) Critical Reviews inMicrobiology 30 (1): 33-54 2004; Zjawiony (2004) J Nat Prod 67 (2):300-310; Carlini & Grossi-de-Sa (2002) Toxicon, 40 (11): 1515-1539;Ussuf et al. (2001) Curr Sci. 80 (7): 847-853; and Vasconcelos &Oliveira (2004) Toxicon 44 (4): 385-403. See also U.S. Pat. No.5,266,317 to Tomalski et al., who disclose genes encodinginsect-specific toxins.

(E) An enzyme responsible for a hyperaccumulation of a monterpene, asesquiterpene, a steroid, hydroxamic acid, a phenylpropanoid derivativeor another non-protein molecule with insecticidal activity.

(F) An enzyme involved in the modification, including thepost-translational modification, of a biologically active molecule; forexample, a glycolytic enzyme, a proteolytic enzyme, a lipolytic enzyme,a nuclease, a cyclase, a transaminase, an esterase, a hydrolase, aphosphatase, a kinase, a phosphorylase, a polymerase, an elastase, achitinase and a glucanase, whether natural or synthetic. See PCTapplication WO 93/02197 in the name of Scott et al., which discloses thenucleotide sequence of a callase gene. DNA molecules which containchitinase-encoding sequences can be obtained, for example, from the ATCCunder Accession Nos. 39637 and 67152. See also Kramer et al., InsectBiochem. Molec. Biol. 23: 691 (1993), who teach the nucleotide sequenceof a cDNA encoding tobacco hookworm chitinase, and Kawalleck et al.,Plant Molec. Biol. 21: 673 (1993), who provide the nucleotide sequenceof the parsley ubi4-2 polyubiquitin gene, and U.S. Pat. Nos. 6,563,020;7,145,060 and 7,087,810.

(G) A molecule that stimulates signal transduction. For example, see thedisclosure by Botella et al., Plant Molec. Biol. 24: 757 (1994), ofnucleotide sequences for mung bean calmodulin cDNA clones, and Griess etal., Plant Physiol. 104: 1467 (1994), who provide the nucleotidesequence of a maize calmodulin cDNA clone.

(H) A hydrophobic moment peptide. See PCT application WO 95/16776 andU.S. Pat. No. 5,580,852 disclosure of peptide derivatives of Tachyplesinwhich inhibit fungal plant pathogens) and PCT application WO 95/18855and U.S. Pat. No. 5,607,914 (teaches synthetic antimicrobial peptidesthat confer disease resistance).

(I) A membrane permease, a channel former or a channel blocker. Forexample, see the disclosure by Jaynes et al., Plant Sci. 89: 43 (1993),of heterologous expression of a cecropin-beta lytic peptide analog torender transgenic tobacco plants resistant to Pseudomonas solanacearum.

(J) A viral-invasive protein or a complex toxin derived therefrom. Forexample, the accumulation of viral coat proteins in transformed plantcells imparts resistance to viral infection and/or disease developmenteffected by the virus from which the coat protein gene is derived, aswell as by related viruses. See Beachy et al., Ann. Rev. Phytopathol.28: 451 (1990). Coat protein-mediated resistance has been conferred upontransformed plants against alfalfa mosaic virus, cucumber mosaic virus,tobacco streak virus, potato virus X, potato virus Y, tobacco etchvirus, tobacco rattle virus and tobacco mosaic virus. Id.

(K) An insect-specific antibody or an immunotoxin derived therefrom.Thus, an antibody targeted to a critical metabolic function in theinsect gut would inactivate an affected enzyme, killing the insect. Cf.Taylor et al., Abstract #497, SEVENTH INT'L SYMPOSIUM ON MOLECULARPLANT-MICROBE INTERACTIONS (Edinburgh, Scotland, 1994) (enzymaticinactivation in transgenic tobacco via production of single-chainantibody fragments).

(L) A virus-specific antibody. See, for example, Tavladoraki et al.,Nature 366: 469 (1993), which shows that transgenic plants expressingrecombinant antibody genes are protected from virus attack.

(M) A developmental-arrestive protein produced in nature by a pathogenor a parasite. Thus, fungal endo alpha-1,4-D-polygalacturonasesfacilitate fungal colonization and plant nutrient release bysolubilizing plant cell wall homo-alpha-1,4-D-galacturonase. See Lamb etal., Bio/Technology 10: 1436 (1992). The cloning and characterization ofa gene which encodes a bean endopolygalacturonase-inhibiting protein isdescribed by Toubart et al., Plant J. 2: 367 (1992).

(N) A developmental-arrestive protein produced in nature by a plant. Forexample, Logemann et al., Bio/Technology 10: 305 (1992), have shown thattransgenic plants expressing the barley ribosome-inactivating gene havean increased resistance to fungal disease.

(O) Genes involved in the Systemic Acquired Resistance (SAR) Responseand/or the pathogenesis related genes. Briggs, S., Current Biology, 5(2)(1995), Pieterse & Van Loon (2004) Curr. Opin. Plant Bio. 7(4):456-64and Somssich (2003) Cell 113(7):815-6.

(P) Antifungal genes (Cornelissen and Melchers, Pl. Physiol.101:709-712, (1993) and Parijs et al., Planta 183:258-264, (1991) andBushnell et al., Can. J. of Plant Path. 20(2):137-149 (1998). Also seeU.S. application Ser. Nos. 09/950,933; 11/619,645; 11/657,710;11/748,994; 11/774,121 and U.S. Pat. Nos. 6,891,085 and 7,306,946.

(Q) Detoxification genes, such as for fumonisin, beauvericin,moniliformin and zearalenone and their structurally related derivatives.For example, see U.S. Pat. Nos. 5,716,820; 5,792,931; 5,798,255;5,846,812; 6,083,736; 6,538,177; 6,388,171 and 6,812,380.

(R) Cystatin and cysteine proteinase inhibitors. See U.S. Pat. No.7,205,453.

(S) Defensin genes. See WO03000863 and U.S. Pat. Nos. 6,911,577;6,855,865; 6,777,592 and 7,238,781.

(T) Genes conferring resistance to nematodes. See e.g. PCT ApplicationWO96/30517; PCT Application WO93/19181, WO 03/033651 and Urwin et al.,Planta 204:472-479 (1998), Williamson (1999) Curr Opin Plant Bio.2(4):327-31; and U.S. Pat. Nos. 6,284,948 and 7,301,069.

(U) Genes that confer resistance to Phytophthora Root Rot, such as theRps 1, Rps 1-a, Rps 1-b, Rps 1-c, Rps 1-d, Rps 1-e, Rps 1-k, Rps 2, Rps3-a, Rps 3-b, Rps 3-c, Rps 4, Rps 5, Rps 6, Rps 7 and other Rps genes.See, for example, Shoemaker et al, Phytophthora Root Rot Resistance GeneMapping in Soybean, Plant Genome IV Conference, San Diego, Calif.(1995).

(V) Genes that confer resistance to Brown Stem Rot, such as described inU.S. Pat. No. 5,689,035 and incorporated by reference for this purpose.

(W) Genes that confer resistance to Colletotrichum, such as described inUS Patent publication US20090035765 and incorporated by reference forthis purpose. This includes the Rcg locus that may be utilized as asingle locus conversion.

2. Transgenes that Confer Tolerance to a Herbicide, for Example:

(A) A herbicide that inhibits the growing point or meristem, such as animidazolinone or a sulfonylurea. Exemplary genes in this category codefor mutant ALS and AHAS enzyme as described, for example, by Lee et al.,EMBO J. 7: 1241 (1988), and Miki et al., Theor. Appl. Genet. 80: 449(1990), respectively. See also, U.S. Pat. Nos. 5,605,011; 5,013,659;5,141,870; 5,767,361; 5,731,180; 5,304,732; 4,761,373; 5,331,107;5,928,937; and 5,378,824; U.S. application Ser. No. 11/683,737, andinternational publication WO 96/33270.

(B) Glyphosate (tolerance imparted by mutant5-enolpyruvl-3-phosphikimate synthase (EPSP) and aroA genes,respectively) and other phosphono compounds such as glufosinate(phosphinothricin acetyl transferase (PAT) and Streptomyceshygroscopicus phosphinothricin acetyl transferase (bar) genes), andpyridinoxy or phenoxy proprionic acids and cyclohexones (ACCaseinhibitor-encoding genes). See, for example, U.S. Pat. No. 4,940,835 toShah et al., which discloses the nucleotide sequence of a form of EPSPSwhich can confer glyphosate tolerance. U.S. Pat. No. 5,627,061 to Barryet al. also describes genes encoding EPSPS enzymes. See also U.S. Pat.Nos. 6,566,587; 6,338,961; 6,248,876 B1; 6,040,497; 5,804,425;5,633,435; 5,145,783; 4,971,908; 5,312,910; 5,188,642; 4,940,835;5,866,775; 6,225,114 B1; 6,130,366; 5,310,667; 4,535,060; 4,769,061;5,633,448; 5,510,471; Re. 36,449; RE 37,287 E; and 5,491,288; andinternational publications EP1173580; WO 01/66704; EP1173581 andEP1173582, which are incorporated herein by reference for this purpose.Glyphosate tolerance is also imparted to plants that express a gene thatencodes a glyphosate oxido-reductase enzyme as described more fully inU.S. Pat. Nos. 5,776,760 and 5,463,175, which are incorporated herein byreference for this purpose. In addition glyphosate tolerance can beimparted to plants by the over expression of genes encoding glyphosateN-acetyltransferase. See, for example, U.S. application Ser. Nos.10/427,692; 10/835,615 and 11/507,751. A DNA molecule encoding a mutantaroA gene can be obtained under ATCC accession No. 39256, and thenucleotide sequence of the mutant gene is disclosed in U.S. Pat. No.4,769,061 to Comai. European Patent Application No. 0 333 033 to Kumadaet al. and U.S. Pat. No. 4,975,374 to Goodman et al. disclose nucleotidesequences of glutamine synthetase genes which confer tolerance toherbicides such as L-phosphinothricin. The nucleotide sequence of aphosphinothricin-acetyl-transferase gene is provided in European PatentNo. 0 242 246 and 0 242 236 to Leemans et al. De Greef et al.,Bio/Technology 7: 61 (1989), describe the production of transgenicplants that express chimeric bar genes coding for phosphinothricinacetyl transferase activity. See also, U.S. Pat. Nos. 5,969,213;5,489,520; 5,550,318; 5,874,265; 5,919,675; 5,561,236; 5,648,477;5,646,024; 6,177,616 B1; and 5,879,903, which are incorporated herein byreference for this purpose. Exemplary genes conferring resistance tophenoxy proprionic acids and cyclohexones, such as sethoxydim andhaloxyfop, are the Acc1-S1, Acc1-S2 and Acc1-S3 genes described byMarshall et al., Theor. Appl. Genet. 83: 435 (1992).

(C) A herbicide that inhibits photosynthesis, such as a triazine (psbAand gs+ genes) and a benzonitrile (nitrilase gene). Przibilla et al.,Plant Cell 3: 169 (1991), describe the transformation of Chlamydomonaswith plasmids encoding mutant psbA genes. Nucleotide sequences fornitrilase genes are disclosed in U.S. Pat. No. 4,810,648 to Stalker, andDNA molecules containing these genes are available under ATCC AccessionNos. 53435, 67441 and 67442. Cloning and expression of DNA coding for aglutathione S-transferase is described by Hayes et al., Biochem. J. 285:173 (1992).

(D) Acetohydroxy acid synthase, which has been found to make plants thatexpress this enzyme resistant to multiple types of herbicides, has beenintroduced into a variety of plants (see, e.g., Hattori et al. (1995)Mol Gen Genet. 246:419). Other genes that confer tolerance to herbicidesinclude: a gene encoding a chimeric protein of rat cytochrome P4507A1and yeast NADPH-cytochrome P450 oxidoreductase (Shiota et al. (1994)Plant Physiol 106:17), genes for glutathione reductase and superoxidedismutase (Aono et al. (1995) Plant Cell Physiol 36:1687, and genes forvarious phosphotransferases (Datta et al. (1992) Plant Mol Biol 20:619).

(E) Protoporphyrinogen oxidase (protox) is necessary for the productionof chlorophyll, which is necessary for all plant survival. The protoxenzyme serves as the target for a variety of herbicidal compounds. Theseherbicides also inhibit growth of all the different species of plantspresent, causing their total destruction. The development of plantscontaining altered protox activity which are tolerant to theseherbicides are described in U.S. Pat. Nos. 6,288,306 B1; 6,282,837 B1;and 5,767,373; and international publication WO 01/12825.

3. Transgenes that Confer or Contribute to an Altered GrainCharacteristic, Such As:

(A) Altered fatty acids, for example, by

-   -   (1) Down-regulation of stearoyl-ACP desaturase to increase        stearic acid content of the plant. See Knultzon et al., Proc.        Natl. Acad. Sci. USA 89: 2624 (1992) and WO99/64579 (Genes for        Desaturases to Alter Lipid Profiles in Corn),    -   (2) Elevating oleic acid via FAD-2 gene modification and/or        decreasing linolenic acid via FAD-3 gene modification (see U.S.        Pat. Nos. 6,063,947; 6,323,392; 6,372,965 and WO 93/11245),    -   (3) Altering conjugated linolenic or linoleic acid content, such        as in WO 01/12800,    -   (4) Altering LEC1, AGP, Dek1, Superal1, mi1 ps, various Ipa        genes such as Ipa1, Ipa3, hpt or hggt. For example, see WO        02/42424, WO 98/22604, WO 03/011015, WO02/057439, WO03/011015,        U.S. Pat. Nos. 6,423,886, 6,197,561, 6,825,397, and U.S.        Application Serial Nos. US2003/0079247, US2003/0204870, and        Rivera-Madrid, R. et al. Proc. Natl. Acad. Sci. 92:5620-5624        (1995).

B) Altered phosphorus content, for example, by the

(1) Introduction of a phytase-encoding gene would enhance breakdown ofphytate, adding more free phosphate to the transformed plant. Forexample, see Van Hartingsveldt et al., Gene 127: 87 (1993), for adisclosure of the nucleotide sequence of an Aspergillus niger phytasegene.

(2) Modulating a gene that reduces phytate content. In maize, this, forexample, could be accomplished, by cloning and then re-introducing DNAassociated with one or more of the alleles, such as the LPA alleles,identified in maize mutants characterized by low levels of phytic acid,such as in WO 05/113778 and/or by altering inositol kinase activity asin WO 02/059324, US2003/0009011, WO 03/027243, US2003/0079247, WO99/05298, U.S. Pat. No. 6,197,561, U.S. Pat. No. 6,291,224, U.S. Pat.No. 6,391,348, WO2002/059324, US2003/0079247, Wo98/45448, WO99/55882,WO01/04147.

(C) Altered carbohydrates affected, for example, by altering a gene foran enzyme that affects the branching pattern of starch or, a genealtering thioredoxin such as NTR and/or TRX (see. (See U.S. Pat. No.6,531,648 which is incorporated by reference for this purpose) and/or agamma zein knock out or mutant such as cs27 or TUSC27 or en27 (See U.S.Pat. No. 6,858,778 and US2005/0160488, US2005/0204418; which areincorporated by reference for this purpose). See Shiroza et al., J.Bacteriol. 170: 810 (1988) (nucleotide sequence of Streptococcus mutansfructosyltransferase gene), Steinmetz et al., Mol. Gen. Genet. 200: 220(1985) (nucleotide sequence of Bacillus subtilis levansucrase gene), Penet al., Bio/Technology 10: 292 (1992) (production of transgenic plantsthat express Bacillus lichenifonnis alpha-amylase), Elliot et al., PlantMolec. Biol. 21: 515 (1993) (nucleotide sequences of tomato invertasegenes), Søgaard et al., J. Biol. Chem. 268: 22480 (1993) (site-directedmutagenesis of barley alpha-amylase gene), and Fisher et al., PlantPhysiol. 102: 1045 (1993) (maize endosperm starch branching enzyme II),WO 99/10498 (improved digestibility and/or starch extraction throughmodification of UDP-D-xylose 4-epimerase, Fragile 1 and 2, Ref1, HCHL,C4H), U.S. Pat. No. 6,232,529 (method of producing high oil seed bymodification of starch levels (AGP)). The fatty acid modification genesmentioned herein may also be used to affect starch content and/orcomposition through the interrelationship of the starch and oilpathways.

(D) Altered antioxidant content or composition, such as alteration oftocopherol or tocotrienols. For example, see U.S. Pat. No. 6,787,683,US2004/0034886 and WO 00/68393 involving the manipulation of antioxidantlevels, and WO 03/082899 through alteration of a homogentisate geranylgeranyl transferase (hggt).

(E) Altered essential seed amino acids. For example, see U.S. Pat. No.6,127,600 (method of increasing accumulation of essential amino acids inseeds), U.S. Pat. No. 6,080,913 (binary methods of increasingaccumulation of essential amino acids in seeds), U.S. Pat. No. 5,990,389(high lysine), WO99/40209 (alteration of amino acid compositions inseeds), WO99/29882 (methods for altering amino acid content ofproteins), U.S. Pat. No. 5,850,016 (alteration of amino acidcompositions in seeds), WO98/20133 (proteins with enhanced levels ofessential amino acids), U.S. Pat. No. 5,885,802 (high methionine), U.S.Pat. No. 5,885,801 (high threonine), U.S. Pat. No. 6,664,445 (plantamino acid biosynthetic enzymes), U.S. Pat. No. 6,459,019 (increasedlysine and threonine), U.S. Pat. No. 6,441,274 (plant tryptophansynthase beta subunit), U.S. Pat. No. 6,346,403 (methionine metabolicenzymes), U.S. Pat. No. 5,939,599 (high sulfur), U.S. Pat. No. 5,912,414(increased methionine), WO98/56935 (plant amino acid biosyntheticenzymes), WO98/45458 (engineered seed protein having higher percentageof essential amino acids), WO98/42831 (increased lysine), U.S. Pat. No.5,633,436 (increasing sulfur amino acid content), U.S. Pat. No.5,559,223 (synthetic storage proteins with defined structure containingprogrammable levels of essential amino acids for improvement of thenutritional value of plants), WO96/01905 (increased threonine),WO95/15392 (increased lysine), US2003/0163838, US2003/0150014,US2004/0068767, U.S. Pat. No. 6,803,498, WO01/79516.

4. Genes that Control Male-Sterility:

There are several methods of conferring genetic male sterilityavailable, such as multiple mutant genes at separate locations withinthe genome that confer male sterility, as disclosed in U.S. Pat. Nos.4,654,465 and 4,727,219 to Brar et al. and chromosomal translocations asdescribed by Patterson in U.S. Pat. Nos. 3,861,709 and 3,710,511. Inaddition to these methods, Albertsen et al., U.S. Pat. No. 5,432,068,describe a system of nuclear male sterility which includes: identifyinga gene which is critical to male fertility; silencing this native genewhich is critical to male fertility; removing the native promoter fromthe essential male fertility gene and replacing it with an induciblepromoter; inserting this genetically engineered gene back into theplant; and thus creating a plant that is male sterile because theinducible promoter is not “on” resulting in the male fertility gene notbeing transcribed. Fertility is restored by inducing, or turning “on”,the promoter, which in turn allows the gene that confers male fertilityto be transcribed.

(A) Introduction of a deacetylase gene under the control of atapetum-specific promoter and with the application of the chemicalN-Ac-PPT (WO 01/29237).

(B) Introduction of various stamen-specific promoters (WO 92/13956, WO92/13957).

(C) Introduction of the barnase and the barstar gene (Paul et al. PlantMol. Biol. 19:611-622, 1992).

For additional examples of nuclear male and female sterility systems andgenes, see also, U.S. Pat. Nos. 5,859,341; 6,297,426; 5,478,369;5,824,524; 5,850,014; and 6,265,640; all of which are herebyincorporated by reference.

5. Genes that create a site for site specific DNA integration. Thisincludes the introduction of FRT sites that may be used in the FLP/FRTsystem and/or Lox sites that may be used in the Cre/Loxp system. Forexample, see Lyznik, et al., Site-Specific Recombination for GeneticEngineering in Plants, Plant Cell Rep (2003) 21:925-932 and WO 99/25821which are hereby incorporated by reference. Other systems that may beused include the Gin recombinase of phage Mu (Maeser et al., 1991; VickiChandler, The Maize Handbook Ch. 118 (Springer-Verlag 1994), the Pinrecombinase of E. coli (Enomoto et al., 1983), and the R/RS system ofthe pSRi plasmid (Araki et al., 1992).6. Genes that affect abiotic stress resistance (including but notlimited to flowering, ear and seed development, enhancement of nitrogenutilization efficiency, altered nitrogen responsiveness, droughtresistance or tolerance, cold resistance or tolerance, and saltresistance or tolerance) and increased yield under stress. For example,see: WO 00/73475 where water use efficiency is altered throughalteration of malate; U.S. Pat. Nos. 5,892,009; 5,965,705; 5,929,305;5,891,859; 6,417,428; 6,664,446; 6,706,866; 6,717,034; 6,801,104;WO2000060089; WO2001026459; WO2001035725; WO2001034726; WO2001035727;WO2001036444; WO2001036597; WO2001036598; WO2002015675; WO2002017430;WO2002077185; WO2002079403; WO2003013227; WO2003013228; WO2003014327;WO2004031349; WO2004076638; WO9809521; and WO9938977 describing genes,including CBF genes and transcription factors effective in mitigatingthe negative effects of freezing, high salinity, and drought on plants,as well as conferring other positive effects on plant phenotype;US2004/0148654 and WO01/36596 where abscisic acid is altered in plantsresulting in improved plant phenotype such as increased yield and/orincreased tolerance to abiotic stress; WO2000/006341, WO04/090143, U.S.application Ser. Nos. 10/817,483 and 09/545,334 where cytokininexpression is modified resulting in plants with increased stresstolerance, such as drought tolerance, and/or increased yield. Also seeWO0202776, WO2003052063, JP2002281975, U.S. Pat. No. 6,084,153,WO0164898, U.S. Pat. No. 6,177,275, and U.S. Pat. No. 6,107,547(enhancement of nitrogen utilization and altered nitrogenresponsiveness). For ethylene alteration, see US20040128719,US20030166197 and WO200032761. For plant transcription factors ortranscriptional regulators of abiotic stress, see e.g. US20040098764 orUS20040078852.

Other genes and transcription factors that affect plant growth andagronomic traits such as yield, flowering, plant growth and/or plantstructure, can be introduced or introgressed into plants, see e.g.WO97/49811 (LHY), WO98/56918 (ESD4), WO97/10339 and U.S. Pat. No.6,573,430 (TFL), U.S. Pat. No. 6,713,663 (FT), WO96/14414 (CON),WO96/38560, WO01/21822 (VRN1), WO00/44918 (VRN2), WO99/49064 (GI),WO00/46358 (FRI), WO97/29123, U.S. Pat. No. 6,794,560, U.S. Pat. No.6,307,126 (GAI), WO99/09174 (D8 and Rht), WO2004076638 and WO2004031349(transcription factors).

Using PH18K6 to Develop Another Maize Plant

Maize varieties such as PH18K6 are typically developed for use in theproduction of hybrid maize varieties. However, varieties such as PH18K6also provide a source of breeding material that may be used to developnew maize inbred varieties. Plant breeding techniques known in the artand used in a maize plant breeding program include, but are not limitedto, recurrent selection, mass selection, bulk selection, mass selection,backcrossing, pedigree breeding, open pollination breeding, restrictionfragment length polymorphism enhanced selection, genetic marker enhancedselection, making double haploids, and transformation. Oftencombinations of these techniques are used. The development of maizehybrids in a maize plant breeding program requires, in general, thedevelopment of homozygous inbred varieties, the crossing of thesevarieties, and the evaluation of the crosses. There are many analyticalmethods available to evaluate the result of a cross. The oldest and mosttraditional method of analysis is the observation of phenotypic traitsbut genotypic analysis may also be used.

This invention is also directed to methods for producing a maize plantby crossing a first parent maize plant with a second parent maize plantwherein either the first or second parent maize plant is a maize plantof the variety PH18K6. The other parent may be any other maize plant,such as another inbred variety or a plant that is part of a synthetic ornatural population. Any such methods using the maize variety PH18K6 arepart of this invention: selfing, sibbing, backcrosses, mass selection,pedigree breeding, bulk selection, hybrid production, crosses topopulations, and the like. These methods are well known in the art andsome of the more commonly used breeding methods are described below.Descriptions of breeding methods can also be found in one of severalreference books (e.g., Allard, Principles of Plant Breeding, 1960;Simmonds, Principles of Crop Improvement, 1979; Fehr, “Breeding Methodsfor Cultivar Development”, Production and Uses, 2^(nd) ed., Wilcoxeditor, 1987 the disclosure of which is incorporated herein byreference).

Pedigree Breeding

Pedigree breeding starts with the crossing of two genotypes, such asPH18K6 and one other inbred variety having one or more desirablecharacteristics that is lacking or which complements PH18K6. If the twooriginal parents do not provide all the desired characteristics, othersources can be included in the breeding population. In the pedigreemethod, superior plants are selfed and selected in successive filialgenerations. In the succeeding filial generations the heterozygouscondition gives way to homogeneous varieties as a result ofself-pollination and selection. Typically in the pedigree method ofbreeding, five or more successive filial generations of selfing andselection is practiced: F1→F2; F2→F3; F3→F4; F4→F5, etc. After asufficient amount of inbreeding, successive filial generations willserve to increase seed of the developed inbred. Preferably, the inbredvariety comprises homozygous alleles at about 95% or more of its loci.

Recurrent Selection and Mass Selection

Recurrent selection is a method used in a plant breeding program toimprove a population of plants. PH18K6 is suitable for use in arecurrent selection program. The method entails individual plants crosspollinating with each other to form progeny. The progeny are grown andthe superior progeny selected by any number of selection methods, whichinclude individual plant, half-sib progeny, full-sib progeny, selfedprogeny and toperossing. The selected progeny are cross pollinated witheach other to form progeny for another population. This population isplanted and again superior plants are selected to cross pollinate witheach other. Recurrent selection is a cyclical process and therefore canbe repeated as many times as desired. The objective of recurrentselection is to improve the traits of a population. The improvedpopulation can then be used as a source of breeding material to obtaininbred varieties to be used in hybrids or used as parents for asynthetic cultivar. A synthetic cultivar is the resultant progeny formedby the intercrossing of several selected inbreds.

PH18K6 is suitable for use in mass selection. Mass selection is a usefultechnique when used in conjunction with molecular marker enhancedselection. In mass selection seeds from individuals are selected basedon phenotype and/or genotype. These selected seeds are then bulked andused to grow the next generation. Bulk selection requires growing apopulation of plants in a bulk plot, allowing the plants toself-pollinate, harvesting the seed in bulk and then using a sample ofthe seed harvested in bulk to plant the next generation. Instead of selfpollination, directed pollination could be used as part of the breedingprogram.

Mutation Breeding

Mutation breeding is one of many methods that could be used to introducenew traits into PH18K6. PH18K6 is suitable for use in a mutationbreeding program. Mutations that occur spontaneously or are artificiallyinduced can be useful sources of variability for a plant breeder. Thegoal of artificial mutagenesis is to increase the rate of mutation for adesired characteristic. Mutation rates can be increased by manydifferent means including temperature, long-term seed storage, tissueculture conditions, radiation; such as X-rays, Gamma rays (e.g. cobalt60 or cesium 137), neutrons, (product of nuclear fission by uranium 235in an atomic reactor), Beta radiation (emitted from radioisotopes suchas phosphorus 32 or carbon 14), or ultraviolet radiation (preferablyfrom 2500 to 2900 nm), or chemical mutagens (such as base analogues(5-bromo-uracil), related compounds (8-ethoxy caffeine), antibiotics(streptonigrin), alkylating agents (sulfur mustards, nitrogen mustards,epoxides, ethylenamines, sulfates, sulfonates, sulfones, lactones),azide, hydroxylamine, nitrous acid, or acridines. Once a desired traitis observed through mutagenesis the trait may then be incorporated intoexisting germplasm by traditional breeding techniques, such asbackcrossing. Details of mutation breeding can be found in “Principlesof Cultivar Development” Fehr, 1993 Macmillan Publishing Company, thedisclosure of which is incorporated herein by reference. In addition,mutations created in other varieties may be used to produce a backcrossconversion of PH18K6 that comprises such mutation.

Production of Double Haploids

The production of double haploids can also be used for the developmentof inbreds in the breeding program. For example, an F1 hybrid for whichPH18K6 is a parent can be used to produce double haploid plants. Doublehaploids are produced by the doubling of a set of chromosomes (1N) froma heterozygous plant to produce a completely homozygous individual. Forexample, see Wan et al., “Efficient Production of Doubled Haploid PlantsThrough Colchicine Treatment of Anther-Derived Maize Callus”,Theoretical and Applied Genetics, 77:889-892, 1989 and US2003/0005479.This can be advantageous because the process omits the generations ofselfing needed to obtain a homozygous plant from a heterozygous source.

Haploid induction systems have been developed for various plants toproduce haploid tissues, plants and seeds. The haploid induction systemcan produce haploid plants from any genotype by crossing a selectedvariety (as female) with an inducer variety. Such inducer varieties formaize include Stock 6 (Coe, 1959, Am. Nat. 93:381-382; Sharkar and Coe,1966, Genetics 54:453-464) RWS (see world wide web sitewww.uni-hohenheim.de/%7Eipspwww/350b/indexe.html#Project3), KEMS(Deimling, Roeber, and Geiger, 1997, Vortr. Pflanzenzuchtg 38:203-224),KMS and ZMS (Chalyk, Bylich & Chebotar, 1994, MNL 68:47; Chalyk &Chebotar, 2000, Plant Breeding 119:363-364), and indeterminategametophyte (ig) mutation (Kermicle 1969 Science 166:1422-1424). Thedisclosures of which are incorporated herein by reference.

Methods for obtaining haploid plants are also disclosed in Kobayashi, M.et al., Journ. of Heredity 71(1):9-14, 1980, Pollacsek, M., Agronomie(Paris) 12(3):247-251, 1992; Cho-Un-Haing et al., Journ. of Plant Biol.,1996, 39(3):185-188; Verdoodt, L., et al., February 1998, 96(2):294-300;Genetic Manipulation in Plant Breeding, Proceedings InternationalSymposium Organized by EUCARPIA, Sep. 8-13, 1985, Berlin, Germany;Chalyk et al., 1994, Maize Genet Coop. Newsletter 68:47; Chalyk, S. T.,1999, Maize Genet. Coop. Newsletter 73:53-54; Coe, R. H., 1959, Am. Nat.93:381-382; Deimling, S. et al., 1997, Vortr. Pflanzenzuchtg 38:203-204;Kato, A., 1999, J. Hered. 90:276-280; Lashermes, P. et al., 1988, Theor.Appl. Genet. 76:570-572 and 76:405-410; Tyrnov, V. S. et al., 1984,Dokl. Akad. Nauk. SSSR 276:735-738; Zabirova, E. R. et al., 1996,Kukuruza I Sorgo N4, 17-19; Aman, M. A., 1978, Indian J. Genet PlantBreed 38:452-457; Chalyk S. T., 1994, Euphytica 79:13-18; Chase, S. S.,1952, Agron. J. 44:263-267; Coe, E. H., 1959, Am. Nat. 93:381-382; Coe,E. H., and Sarkar, K. R., 1964 J. Hered. 55:231-233; Greenblatt, I. M.and Bock, M., 1967, J. Hered. 58:9-13; Kato, A., 1990, Maize Genet.Coop. Newsletter 65:109-110; Kato, A., 1997, Sex. Plant Reprod.10:96-100; Nanda, D. K. and Chase, S. S., 1966, Crop Sci. 6:213-215;Sarkar, K. R. and Coe, E. H., 1966, Genetics 54:453-464; Sarkar, K. R.and Coe, E. H., 1971, Crop Sci. 11:543-544; Sarkar, K. R. and Sachan J.K. S., 1972, Indian J. Agric. Sci. 42:781-786; Kermicle J. L., 1969,Mehta Yeshwant, M. R., Genetics and Molecular Biology, September 2000,23(3):617-622; Tahir, M. S. et al. Pakistan Journal of Scientific andIndustrial Research, August 2000, 43(4):258-261; Knox, R. E. et al.Plant Breeding, August 2000, 119(4):289-298; U.S. Pat. No. 5,639,951 andU.S. patent application Ser. No. 10/121,200, the disclosures of whichare incorporated herein by reference.

Thus, an embodiment of this invention is a process for making ahomozygous PH18K6 progeny plant substantially similar to PH18K6 byproducing or obtaining a seed from the cross of PH18K6 and another maizeplant and applying double haploid methods to the F1 seed or F1 plant orto any successive filial generation. Such methods decrease the number ofgenerations required to produce an inbred with similar genetics orcharacteristics to PH18K6. See Bernardo, R. and Kahler, A. L., Theor.Appl. Genet. 102:986-992, 2001.

In particular, a process of making seed substantially retaining themolecular marker profile of maize variety PH18K6 is contemplated, suchprocess comprising obtaining or producing F1 hybrid seed for which maizevariety PH18K6 is a parent, inducing double haploids to create progenywithout the occurrence of meiotic segregation, obtaining the molecularmarker profile of maize variety PH18K6, and selecting progeny thatretain the molecular marker profile of PH18K6.

Use of PH18K6 in Tissue Culture

This invention is also directed to the use of PH18K6 in tissue culture.As used herein, the term “tissue culture” includes plant protoplasts,plant cell tissue culture, cultured microspores, plant calli, plantclumps, and the like. As used herein, phrases such as “growing the seed”or “grown from the seed” include embryo rescue, isolation of cells fromseed for use in tissue culture, as well as traditional growing methods.

Duncan, Williams, Zehr, and Widholm, Planta (1985) 165:322-332 reflectsthat 97% of the plants cultured that produced callus were capable ofplant regeneration. Subsequent experiments with both inbreds and hybridsproduced 91% regenerable callus that produced plants. In a further studyin 1988, Songstad, Duncan & Widholm in Plant Cell Reports (1988),7:262-265 reports several media additions that enhance regenerability ofcallus of two inbred varieties. Other published reports also indicatedthat “nontraditional” tissues are capable of producing somaticembryogenesis and plant regeneration. K. P. Rao, et al., Maize GeneticsCooperation Newsletter, 60:64-65 (1986), refers to somatic embryogenesisfrom glume callus cultures and B. V. Conger, et al., Plant Cell Reports,6:345-347 (1987) indicates somatic embryogenesis from the tissuecultures of maize leaf segments. Thus, it is clear from the literaturethat the state of the art is such that these methods of obtaining plantsare, and were, “conventional” in the sense that they are routinely usedand have a very high rate of success.

Tissue culture of maize, including tassel/anther culture, is describedin U.S. 2002/0062506A1 and European Patent Application, publicationEP0160,390, each of which are incorporated herein by reference for thispurpose. Maize tissue culture procedures are also described in Green andRhodes, “Plant Regeneration in Tissue Culture of Maize,” Maize forBiological Research (Plant Molecular Biology Association,Charlottesville, Va. 1982, at 367-372) and in Duncan, et al., “TheProduction of Callus Capable of Plant Regeneration from Immature Embryosof Numerous Zea Mays Genotypes,” 165 Planta 322-332 (1985). Thus,another aspect of this invention is to provide cells which upon growthand differentiation produce maize plants having the genotype and/orphenotypic characteristics of variety PH18K6.

INDUSTRIAL APPLICABILITY

Maize is used as human food, livestock feed, and as raw material inindustry. The food uses of maize, in addition to human consumption ofmaize kernels, include both products of dry- and wet-milling industries.The principal products of maize dry milling are grits, meal and flour.The maize wet-milling industry can provide maize starch, maize syrups,and dextrose for food use. Maize oil is recovered from maize germ, whichis a by-product of both dry- and wet-milling industries.

Maize, including both grain and non-grain portions of the plant, is alsoused extensively as livestock feed, primarily for beef cattle, dairycattle, hogs, and poultry.

Industrial uses of maize include production of ethanol, maize starch inthe wet-milling industry and maize flour in the dry-milling industry.The industrial applications of maize starch and flour are based onfunctional properties, such as viscosity, film formation, adhesiveproperties, and ability to suspend particles. The maize starch and flourhave application in the paper and textile industries. Other industrialuses include applications in adhesives, building materials, foundrybinders, laundry starches, explosives, oil-well muds, and other miningapplications.

Plant parts other than the grain of maize are also used in industry: forexample, stalks and husks are made into paper and wallboard and cobs areused for fuel and to make charcoal.

The seed of maize variety PH18K6, the plant produced from the seed, thehybrid maize plant produced from the crossing of the variety, hybridseed, and various parts of the hybrid maize plant and transgenicversions of the foregoing, can be utilized for human food, livestockfeed, and as a raw material in industry.

TABLE 1 VARIETY DESCRIPTION INFORMATION - PH18K6 1. TYPE: (Describeintermediate types in comments section) 1 = Sweet, 2 = Dent, 3 = Flint,4 = Flour, 5 = Pop and 6 = Ornamental. 3 Comments: Flint Like 2.MATURITY: Days Heat Units Emergence to 50% of plants in silk 51.0 1300Emergence to 50% of plants in pollen shed 51.0 1300 10% to 90% pollenshed 0.5 12 3. PLANT Value StDev Number Plant Height (to tassel tip)(cm) 80.0 3.63 18 Ear Height (to base of top ear node) 24.0 2.22 18Length of Top Ear Internode (cm) 16.0 1.08 18 ** Average Number ofTillers per Plant 0.0 0.00 2 ** Average Number of Ears per Stalk 0.90.00 2 Anthocyanin of Brace Roots: 1 = Absent, 2 = Faint, 4 3 =Moderate, 4 = Dark 4. LEAF: Width of Ear Node Leaf (cm) 8.7 0.57 18Length of Ear Node Leaf (cm) 78.8 3.60 18 Number of Leaves above Top Ear6.3 0.67 18 Leaf Angle: (at anthesis, 2nd leaf above ear to 22.5 3.93 18stalk above leaf) (Degrees) Leaf Color: V. Dark Green * Munsell: 5GY36Leaf Sheath Pubescence: 1 = none to 9 = like peach fuzz 4 5. TASSEL:Number of Primary Lateral Branches 5.2 1.63 18 Branch Angle from CentralSpike (Degrees) 23.9 7.78 18 Tassel Length: (from peduncle node totassel tip) (cm) 52.2 2.65 18 Peduncle Length: (From top leaf node tolower branch)(cm) 21.3 2.30 18 Pollen Shed: 0 = male sterile, 9 = heavyshed 6 Bar Glumes (glume bands): 1 = absent, 2 = present 1 Anther Color:Pink Orange * Munsell: 2.5YR48 Glume Color: Red * Munsell: 10RP38 6a.EAR (Unhusked ear) Silk color: (3 days after silk emergence) Light Red *Munsell: 10RP58 Fresh husk color: Med. Green * Munsell: 2.5GY66 Dry huskcolor: (65 days after 50% silking) Buff * Munsell: 10RP38 Ear positionat dry husk stage: 1 = Upright, 2 = Horizontal, 2 3 = Pendant HuskTightness: (1 = very loose, 9 = very tight) 7 Husk Extension (atharvest): 1 = short(ears exposed), 2 2 = medium (<8 cm), 3 = long (8-10cm), 4 = v. long (>10 cm) 6b. EAR (Husked ear data) Shank Length (cm):7.4 2.64 18 Ear Length (cm): 14.1 1.08 18 Ear Diameter at mid-point (mm)36.3 1.19 18 Ear Weight (gm): 97.0 11.54 18 Number of Kernel Rows: 13.11.23 18 Kernel Rows: 1 = indistinct, 2 = distinct 2 Row Alignment: 1 =straight, 2 = slightly curved, 3 = spiral 2 Ear Taper: 1 = slightcylind., 2 = average, 3 = extreme conic. 2 7. KERNEL (Dried): KernelLength (mm): 10.3 0.75 18 Kernel Width (mm): 7.7 0.57 18 KernelThickness (mm): 4.2 0.43 18 ** Weight per 100 Kernels (unsized sample)(gm): 23.0 0.00 2 ** Round Kernels (shape grade) (%) 28.6 5.78 2Aleurone Color Pattern: 1 = homozygous, 2 = segregating 1 EndospermType: 1 = sweet (su1), 2 = extra sweet (sh2), 3 = normal starch, 3 4 =high amylose starch, 5 = waxy starch, 6 = high protein, 7 = high lysine,8 = super sweet (se), 9 = high oil, 10 = other Aleurone Color: Yellow *Munsell: 10YR714 Hard Endosperm Color: Yellow * Munsell: 10YR714 8. COB:Cob Diameter at mid-point (mm): 19.7 1.13 18 Cob Color: White * Munsell:5Y91 Number is the number of individual plants that were scored. Valueis an average if more than one plant or plot is scored. * Munsell GlossyBook of color, (A standard color reference). Kollmorgen Inst. Corp. NewWindsor, NY. **Sample number reflects the number of plots where thetrait(s) was observed and not the number of individual plants scored.

TABLE 2 Inbred PH18K6 platform BLUP breeding values Weighted Trait BLUPvalue ANTROT 5.0 BORBMN 55.7 BRLPNE 64.4 BRLPNL 92.3 BRTSTK 96.0 DIGENG1812.7 EARHT 44.5 ERTLPN 86.1 EXTSTR 66.7 FUSERS 3.8 GDUSHD 125.5 GDUSLK123.5 GIBERS 7.8 GLFSPT 4.7 GOSWLT 6.5 HDSMT 94.2 HSKCVR 5.3 HTFRM 38.3LRTLPN 78.2 MILKLN 41.8 MST 19.2 NLFBLT 6.0 PLTHT 114.6 STAGRN 4.0STKCTE 92.5 STLLPN 78.9 STLPCN 94.1 TSTWT 57.9 TSTWTN 57.5 YIELD 192.3

TABLE 3 Inbred PH18K6 as parent in hybrid BRLPNE BRLPNL BRTSTK ftnoteBLUP SE BLUP SE BLUP SE Hybrid1 (a,b) 95.1 1.7 Hybrid2 (a,b) 60.0 6.580.4 4.9 95.4 1.7 Hybrid3 (a) 59.8 5.6 82.9 3.7 96.0 1.5 Hybrid4 (a,b)96.6 1.5 DIGENG EARHT ERTLPN ftnote BLUP SE BLUP SE BLUP SE Hybrid1(a,b) 47.8 0.5 88.8 2.9 Hybrid2 (a,b) 1810.6 4.7 47.9 0.5 87.1 2.8Hybrid3 (a) 1811.5 4.1 47.7 0.7 84.7 2.9 Hybrid4 (a,b) 49.3 0.7 84.3 2.9EXTSTR GDUSHD GDUSLK ftnote BLUP SE BLUP SE BLUP SE Hybrid1 (a,b) 128.20.8 126.1 0.6 Hybrid2 (a,b) 66.2 0.3 127.0 0.8 125.0 0.6 Hybrid3 (a)67.3 0.2 131.3 0.8 130.1 0.8 Hybrid4 (a,b) 131.0 0.8 129.6 0.8 GLFSPTGOSWLT HDSMT ftnote BLUP SE BLUP SE BLUP SE Hybrid1 (a,b) Hybrid2 (a,b)5.0 0.3 6.5 0.4 93.4 3.5 Hybrid3 (a) 4.5 0.2 6.7 0.3 94.3 4.3 Hybrid4(a,b) 4.8 0.3 HTFRM LRTLPN MILKLN ftnote BLUP SE BLUP SE BLUP SE Hybrid1(a,b) 79.6 4.2 40.8 2.8 Hybrid2 (a,b) 38.2 0.1 85.8 4.0 40.3 2.8 Hybrid3(a) 38.4 0.1 85.2 5.2 Hybrid4 (a,b) 84.9 5.3 MST NLFBLT PLTHT ftnoteBLUP SE BLUP SE BLUP SE Hybrid1 (a,b) 19.4 0.1 5.8 0.4 118.0 0.7 Hybrid2(a,b) 18.9 0.1 5.3 0.3 116.1 0.7 Hybrid3 (a) 18.8 0.1 6.3 0.3 118.9 0.9Hybrid4 (a,b) 19.1 0.1 6.1 0.3 119.0 0.9 STAGRN STKCTE STLLPN ftnoteBLUP SE BLUP SE BLUP SE Hybrid1 (a,b) 4.6 0.3 91.6 0.6 Hybrid2 (a,b) 4.30.4 90.8 0.5 88.8 5.0 Hybrid3 (a) 4.2 0.2 87.5 0.6 78.7 4.2 Hybrid4(a,b) 4.8 0.3 87.4 0.6 STLPCN TSTWT TSTWTN ftnote BLUP SE BLUP SE BLUPSE Hybrid1 (a,b) 90.8 2.9 57.6 0.1 57.0 0.1 Hybrid2 (a,b) 90.8 2.8 57.20.1 56.6 0.1 Hybrid3 (a) 87.1 3.0 57.3 0.1 57.0 0.1 Hybrid4 (a,b) 84.63.0 57.3 0.1 56.9 0.1 YIELD ftnote BLUP SE Hybrid1 (a,b) 197.8 1.5Hybrid2 (a,b) 191.7 1.5 Hybrid3 (a) 194.0 1.6 Hybrid4 (a,b) 196.1 1.6 awherein inbred comprises a trait conversion conferring insect control bwherein inbred comprises a trait conversion conferring herbicidetolerance c wherein inbred comprises a trait conversion conferringdisease control

DEPOSITS

Applicant has made a deposit of at least 2500 seeds of Maize VarietyPH18K6 with the American Type Culture Collection (ATCC), 10801University Boulevard, Manassas, Va. 20110-2209, USA, with ATCC DepositNo. PTA-120185. The seeds deposited with the ATCC on Apr. 12, 2013 wereobtained from the seed of the variety maintained by Pioneer Hi-BredInternational, Inc., 7250 NW 62^(nd) Avenue, Johnston, Iowa, 50131 sinceprior to the filing date of this application. Access to this seed willbe available during the pendency of the application to the Commissionerof Patents and Trademarks and persons determined by the Commissioner tobe entitled thereto upon request. Upon allowance of any claims in theapplication, the Applicant will make the deposit available to the publicpursuant to 37 C.F.R. §1.808. This deposit of the Maize Variety PH18K6will be maintained in the ATCC depository, which is a public depository,for a period of 30 years, or 5 years after the most recent request, orfor the enforceable life of the patent, whichever is longer, and will bereplaced if it becomes nonviable during that period. Additionally,Applicant has or will satisfy all of the requirements of 37 C.F.R.§§1.801-1.809, including providing an indication of the viability of thesample upon deposit. Applicant has no authority to waive anyrestrictions imposed by law on the transfer of biological material orits transportation in commerce. Applicant does not waive anyinfringement of rights granted under this patent or under the PlantVariety Protection Act (7 USC 2321 et seq.).

What is claimed is:
 1. A seed of inbred maize variety PH18K6,representative seed of said variety having been deposited under ATCCaccession number PTA-120185.
 2. A method of collecting molecular datacomprising isolating nucleic acids contained in the seed of claim 1,analyzing said nucleic acids, and recording data based on the nucleicacids.
 3. A plant, plant part, or cell produced by growing the seed ofinbred maize variety of claim
 1. 4. A method of collecting moleculardata comprising isolating nucleic acids contained in the plant, plantpart, or cell of claim 3, analyzing said nucleic acids, and recordingdata based on the nucleic acids.
 5. A maize seed produced by crossingthe plant or plant part of claim 3 with a different maize plant.
 6. Amaize plant produced by growing the maize seed of claim
 5. 7. A methodfor producing a second maize plant comprising applying plant breedingtechniques to a first maize plant, or parts thereof, wherein said firstmaize plant is the maize plant of claim 6, and wherein application ofsaid techniques results in the production of said second maize plant. 8.The method of claim 7, further defined as producing a maize plantderived from the inbred maize variety PH18K6, the method comprising thesteps of: (a) crossing said first maize plant with itself or anothermaize plant to produce seed of a subsequent generation; (b) harvestingand planting the seed of the subsequent generation to produce at leastone plant of the subsequent generation; and (c) repeating steps (a) and(b) for an additional 2-10 generations to produce a maize plant derivedfrom maize variety PH18K6.
 9. An inbred maize plant derived from theinbred maize variety PH18K6 produced by the method of claim 8, whereinsaid inbred maize plant has essentially the same morphological andphysiological characteristics as inbred maize variety PH18K6 when grownunder the same environmental conditions.
 10. The method of claim 7,further defined as producing an inbred maize plant derived from maizevariety PH18K6, the method comprising the steps of: (a) crossing saidfirst maize plant with an inducer variety to produce haploid seed; and(b) doubling the haploid seed to produce an inbred maize plant derivedfrom maize variety PH18K6.
 11. The inbred maize plant derived from theinbred maize variety PH18K6 produced by the method of claim 10, whereinsaid inbred maize plant has essentially the same morphological andphysiological characteristics as inbred maize variety PH18K6 when grownunder the same environmental conditions.
 12. A converted seed of inbredmaize variety PH18K6, representative seed of said variety having beendeposited under ATCC accession number PTA-120185; wherein said convertedseed comprises a locus conversion; and wherein said converted seed growsinto a plant having essentially the same morphological and physiologicalcharacteristics as maize variety PH18K6 when grown under the sameenvironmental conditions.
 13. The converted seed of claim 12, whereinthe locus conversion confers a trait selected from the group consistingof male sterility, site-specific recombination, abiotic stresstolerance, altered phosphorus, altered antioxidants, altered fattyacids, altered essential amino acids, altered carbohydrates, herbicidetolerance, insect resistance and disease resistance.
 14. A method ofcollecting molecular data comprising isolating nucleic acids containedin the converted seed of claim 12, analyzing said nucleic acids, andrecording data based on the nucleic acids.
 15. A plant or plant partproduced by growing the converted seed of the inbred maize varietyPH18K6 of claim
 12. 16. A method of collecting molecular data comprisingisolating nucleic acids contained in the plant, plant part, or cell ofclaim 15, analyzing said nucleic acids, and recording data based on thenucleic acids.
 17. A maize seed produced by crossing the plant or plantpart of claim 15 with a different maize plant.
 18. A maize plantproduced by growing the seed of claim
 17. 19. A method for producing asecond maize plant comprising applying plant breeding techniques to afirst maize plant, or parts thereof, wherein said first maize plant isthe maize plant of claim 18, and wherein application of said techniquesresults in the production of said second maize plant.
 20. The method ofclaim 19, further defined as producing a maize plant, the methodcomprising the steps of: (a) crossing said first maize plant with itselfor another maize plant to produce seed of a subsequent generation; (b)harvesting and planting the seed of the subsequent generation to produceat least one plant of the subsequent generation; and (c) repeating steps(a) and (b) for an additional 2-10 generations to produce a maize plant.21. An inbred maize plant derived from the inbred maize variety PH18K6produced by the method of claim 20, wherein said inbred maize plant hasessentially the same morphological and physiological characteristics asinbred maize variety PH18K6 when grown under the same environmentalconditions.
 22. The method of claim 19, further defined as producing amaize plant, the method comprising the steps of: (a) crossing said firstmaize plant with an inducer variety to produce haploid seed; and (b)doubling the haploid seed to produce an inbred maize plant.
 23. Theinbred maize plant derived from the inbred maize variety PH18K6 producedby the method of claim 22, wherein said inbred maize plant hasessentially the same morphological and physiological characteristics asinbred maize variety PH18K6 when grown under the same environmentalconditions.